- This also introduces some tests to make sure that our cache config
stays intact with the configuration. We can probably remove this at some
point however.

- experiment for user acceptance.

- allows us to measure acceptance of invites with avatars

- This introduces a new concept to define enabled/disabled states for
experiments, an improved exclusion interface, and new rspec tooling.

This reverts merge request !52268

- This introduces a new concept to define enabled/disabled states for
experiments, an improved exclusion interface, and new rspec tooling.

- With some minor spec adjustments

- Version 0.4.3 has improved caching behavior and order of operations
when determining the variant.

- This makes the configuration easier to test, improves those tests, and
provides a base class that all future experiments can use.