Add segments filter in assignment view

[acelaya]

depends on #6687 and #6688

Add a fourth filtering dropdown for groups or sections (AKA segments), which is only displayed when the assignment view is loaded.

For now, we only display this filter if the assignment has auto-grading enabled, to reduce potentially affected users in case of an issue, but we'll eventually enable it for any assignment, as it's generally useful.

Its selected values are used to filter the students list and the students metrics.

segments-filter-2024-09-18_10.31.19.mp4

Note

This PR is easier to review ignoring whitespaces

Testing steps

1. Check out this branch
2. Go to https://hypothesis.instructure.com/courses/319/assignments/7296 and open the dashboard. It should show a fourth filtering dropdown, right before students one.
3. Changing values in that dropdown should affect the list of users in the table and the users dropdown.
4. Go to another assignment without auto-grading enabled. You should not see the segments dropdown.
5. Go to any other view. You should not see the segments dropdown.

[acelaya]

We'll merge this PR into #6688, and then merge both together into main.

[robertknight]

This looks good with a few minor comments. One general thing I would be careful about is reusing string literals used as type discriminators to construct UI text, and especially constructing derivatives to handle pluralization etc. Usually a developer would expect that changing such a literal would not break anything as long as they do a simple update (search + replace) for references in the code.