feat: add contains constraint type

[markphelps]

Re: flipt-io/flipt#4018

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.71%. Comparing base (f701007) to head (a138981).
Report is 96 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #856      +/-   ##
==========================================
- Coverage   80.36%   77.71%   -2.65%     
==========================================
  Files           8        8              
  Lines        4165     4335     +170     
==========================================
+ Hits         3347     3369      +22     
- Misses        818      966     +148     

☔ 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.