Complete the MFE conversion process for edx-platform

[kdmccormick]

• Complete all linked sub-issues
• Continue using the MFE Rewrite Tracker and linked resources to identify, track, and monitor legacy frontend progress, adding items below or creating issues as neccessary.
• Convert program dashboard to MFE
• Convert course certificates to MFE
• Convert custom course tabs to MFE
• Convert instructor dashboard to MFE
• Deprecate or convert LMS "About Course" page to MFE
• Deprecate or convert LMS "Explore New" page to MFE
• Search for any remaining legacy LMS pages that need conversion
• Remove remaining unused legacy frontends
• Clean up frontend tooling, config, CI, etc.