Session onboarding improvements

[tim-schilling]

References #617

• Make the session admin easier to use
• Generate score column for each text based answer on single scorer csv.
• Show an message when a user hasn't set their availability, but has applied.
• Clean up CustomUser str dunder method.
• Remove the available project inline in favor of filter_horizontal.
• Improve the user selection for Session Membership in admin.

New session admin view

Notification for when a user doesn't have availability set

New Project Preferences selection

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.70%. Comparing base (ce1e79b) to head (29db55b).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #619      +/-   ##
===========================================
+ Coverage    94.61%   94.70%   +0.08%     
===========================================
  Files          154      157       +3     
  Lines         6710     6755      +45     
  Branches       217      222       +5     
===========================================
+ Hits          6349     6397      +48     
+ Misses         323      321       -2     
+ Partials        38       37       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.