chore: add __init__.py to feature flag test module

[danieljhegeman]

Reason for Change

• Optimize recently-introduced 'feature flag' service
  • Reduce code complexity
  • Add __init__.py to make sure the patch() call works on the given CorporaConfig path so that the related unit tests can be run individually using python -m pytest .... In its current state this does not work.

Changes

• remove the FeatureFlag: Literal[]
• modify the FeatureFlagValues to inherit from enum.Enum so as to still enforce approved feature flag values without having to use an extra FeatureFlag entity.
• rename FeatureFlagValues -> FeatureFlag

Testing steps

• Tests updated

Checklist 🛎️

• Add product, design, and eng as reviewers for rdev review

• For UI changes, add screenshots/videos, so the reviewers know what you expect them to see

• For UI changes, add e2e tests to prevent regressions

Notes for Reviewer

[github-actions]

Deployment Summary

• backend_url: https://pr-6209-backend.rdev.single-cell.czi.technology
• frontend_url: https://pr-6209-frontend.rdev.single-cell.czi.technology
• delete_db_task_definition_arn: arn:aws:ecs:us-west-2:***:task-definition/dp-rdev-pr-6209-deletion:1
• migrate_db_task_definition_arn: arn:aws:ecs:us-west-2:***:task-definition/dp-rdev-pr-6209-migration:1

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (1e902ab) 91.60% compared to head (efe81b4) 91.79%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
backend/layers/processing/schema_migration.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6209      +/-   ##
==========================================
+ Coverage   91.60%   91.79%   +0.19%     
==========================================
  Files         175      175              
  Lines       14232    14206      -26     
==========================================
+ Hits        13037    13041       +4     
+ Misses       1195     1165      -30     

Flag	Coverage Δ
unittests	91.79% <98.00%> (+0.19%)	⬆️

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