Fix Azure CLI extension GitHub release notes

[Chien Yuan Chang (chienyuanchang)]

Summary

• extract the selected Azure CLI extension version section from HISTORY.rst
• validate that extension notes are dated and non-empty
• publish the generated Markdown through gh release create --notes-file
• add regression tests for note generation and missing versions

Validation

• python -m pytest packages/standalone/tests/unit/test_validate_release.py -q (17 passed)
• python -m ruff check scripts/validate_release.py packages/standalone/tests/unit/test_validate_release.py
• git diff --check

Note

The full scripts/ci.sh suite currently has an unrelated failure in test_analyze_usage_prints_inline_usage_to_stderr_without_changing_json: Rich wraps sample.pdf across lines in the long pytest temporary path.

[Chien Yuan Chang (chienyuanchang)]

Included unchanged in #35 (commit 163878c), which also contains the release dependency fix and beta-3 package metadata. Closing this separate PR as superseded.