[Docs] Update admin center instructions: add new image and revise classic image text

[nirav-raval]

The update includes:

• Added instructions and image for new power platform admin center
• Renamed old image and alt text

[learn-build-service-prod]

Learn Build status updates of commit baa7ab2:

💡 Validation status: suggestions

File	Status	Preview URL	Details
power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png	💡Suggestion		Details
power-platform/admin/managed-environment-enable.md	✅Succeeded
power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png	✅Succeeded
power-platform/admin/media/managed-environment-enable/managed-environments-enable.png	✅Succeeded	n/a (file deleted or renamed)

power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png

• Line 0, Column 0: [Suggestion: image-name-invalid-character - See documentation] Only lowercase letters, numbers, and hyphens are allowed in image names.
• Line 0, Column 0: [Suggestion: image-name-incomplete - See documentation] The image name contains an incomplete word, misspelled word, acronym, or abbreviation that is disallowed.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[learn-build-service-prod]

Learn Build status updates of commit 4aef493:

💡 Validation status: suggestions

File	Status	Preview URL	Details
power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png	💡Suggestion		Details
power-platform/admin/managed-environment-enable.md	✅Succeeded
power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png	✅Succeeded
power-platform/admin/media/managed-environment-enable/managed-environments-enable.png	✅Succeeded	n/a (file deleted or renamed)

power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png

• Line 0, Column 0: [Suggestion: image-name-invalid-character - See documentation] Only lowercase letters, numbers, and hyphens are allowed in image names.
• Line 0, Column 0: [Suggestion: image-name-incomplete - See documentation] The image name contains an incomplete word, misspelled word, acronym, or abbreviation that is disallowed.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[learn-build-service-prod]

Learn Build status updates of commit 1e7fb8a:

💡 Validation status: suggestions

File	Status	Preview URL	Details
power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png	💡Suggestion		Details
power-platform/admin/managed-environment-enable.md	✅Succeeded
power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png	✅Succeeded
power-platform/admin/media/managed-environment-enable/managed-environments-enable.png	✅Succeeded	n/a (file deleted or renamed)

power-platform/admin/media/managed-environment-enable/new_managed-environments-enable.png

• Line 0, Column 0: [Suggestion: image-name-invalid-character - See documentation] Only lowercase letters, numbers, and hyphens are allowed in image names.
• Line 0, Column 0: [Suggestion: image-name-incomplete - See documentation] The image name contains an incomplete word, misspelled word, acronym, or abbreviation that is disallowed.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[learn-build-service-prod]

Learn Build status updates of commit a4e842f:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
power-platform/admin/managed-environment-enable.md	⚠️Warning		Details
power-platform/admin/media/managed-environment-enable/latest_managed-environments-enable.png	💡Suggestion		Details
power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png	✅Succeeded
power-platform/admin/media/managed-environment-enable/managed-environments-enable.png	✅Succeeded	n/a (file deleted or renamed)

power-platform/admin/managed-environment-enable.md

• Line 44, Column 1: [Warning: file-not-found - See documentation] Invalid file link: 'media/managed-environment-enable/new_managed-environments-enable.png'.

power-platform/admin/media/managed-environment-enable/latest_managed-environments-enable.png

• Line 0, Column 0: [Suggestion: image-name-invalid-character - See documentation] Only lowercase letters, numbers, and hyphens are allowed in image names.
• Line 0, Column 0: [Suggestion: image-name-incomplete - See documentation] The image name contains an incomplete word, misspelled word, acronym, or abbreviation that is disallowed.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.

[learn-build-service-prod]

Learn Build status updates of commit 6e42c9a:

💡 Validation status: suggestions

File	Status	Preview URL	Details
power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png	💡Suggestion		Details
power-platform/admin/managed-environment-enable.md	✅Succeeded
power-platform/admin/media/managed-environment-enable/managed-environments-enable.png	✅Succeeded

power-platform/admin/media/managed-environment-enable/classic_managed-environments-enable.png

• Line 0, Column 0: [Suggestion: image-name-invalid-character - See documentation] Only lowercase letters, numbers, and hyphens are allowed in image names.
• Line 0, Column 0: [Suggestion: image-name-incomplete - See documentation] The image name contains an incomplete word, misspelled word, acronym, or abbreviation that is disallowed.

For more details, please refer to the build report.

Note: Your PR may contain errors or warnings or suggestions unrelated to the files you changed. This happens when external dependencies like GitHub alias, Microsoft alias, cross repo links are updated. Please use these instructions to resolve them.