feat: confidence flag api

[andreas-karlsson]

Hi There, I just made a Pull Request!

This PR adds an API to resolve flags directly from the Confidence object.

:heavy_check_mark: Checklist

• [ ] All tests are passing
• [ ] Relevant documentation updated
• [ ] linter/style run on changed files
• [ ] Tests added for new functionality
• [ ] Regression tests added for bug fixes
• [ ] Tested in a corresponding example app

[nicklasl]

Also verify that we have tests for apply (both backend and clients).