Project leads: Add page for reviewing educator labels

[kevinrobinson]

Who is this PR for?

project leads

What problem does this PR fix?

Within Student Insights "labels" are used as fine-grained feature switches for specific features, staged rollouts, etc. Revising these often requires communication and collaboration, so it doesn't make sense to make this entirely self-serve for project leads. But for seasonal or recurring kinds of changes, where updates are fairly well-understood, a first step towards self-serve is allowing project leads to review these settings directly.

What does this PR do?

Adds a new admin page showing the list of labels, and which educators have them applied. This information is visible in the existing admin pages, but this focuses on the labels as the concept (eg, "show me who has access to finalize class lists as a principal").

Screenshot (if adding a client-side feature)

Checklists

Which features or pages does this PR touch?

• Districtwide
• Educator: Labels review

Does this PR use tests to help verify we can deploy these changes quickly and confidently?

• Included specs for changes
• Improved specs for existing code in need of better test coverage
• Manual testing made more sense here

[kevinrobinson]

selfie