Limit the size of a set at some level

[jnunemaker]

The individual actor and group gates are not made to store hundreds or thousands of values. We should limit the size these sets can grow to in an effort to help prevent people from hurting themselves. This check could happen at enable time to prevent enabling more than 1k or some number of individual elements in a set.

[rstawarz]

👋 Is the plan not to support > 1k flipper gates for actors?

We were looking at migrating to flipper from our custom feature flag solution, but it appears that there isn't a way to configure it to not load every actor gate into memory - is that really the case?

[jnunemaker]

Solved by #847