implement a more cohesive feature flags struct for use in the project #563
Description
change our env-variable-based feature flag (the rbac thing) to something more maintainable. It should be possible to (from Go language semantics, and not with grep) discover the full set of flags in existence. Testing (in envtest, in deployed rhoai) with various combinations of flag values should be made straightforward. Consult Andy who mentioned bad experience with env vars from previous work. See also GitHub issue about creating helper to uniformly parse bool values
Decided in meeting https://docs.google.com/document/d/1J1qj09NIFpmKrZWAAHTmskO1nqaRnpAcONM6Isnqvqk/edit?tab=t.0