Use component.StabilityLevel for entity stability

[dmathieu]

Right now, the entity is using string for its stability field, which prevents validating that the value is within the enum.
This changes it to a component.StabilityLevel.

[dmathieu]

This change means the generated doc now capitalized the stability. I can lowercase, but this feels more readable to me.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.81%. Comparing base (8ba3ae3) to head (cb41e8d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14425      +/-   ##
==========================================
+ Coverage   91.80%   91.81%   +0.01%     
==========================================
  Files         677      677              
  Lines       42608    42608              
==========================================
+ Hits        39116    39122       +6     
+ Misses       2429     2425       -4     
+ Partials     1063     1061       -2     

☔ 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.