[FLI-671] Feature Request: Allow entityID as rule/rollout segment

[markphelps]

Discussed in #2069

^{Originally posted by graytonio September 1, 2023}
When creating an evaluation rule or rollout for a flag we are able to select a segment as the "target" of the rule and in most cases this is perfect. However in some circumstances I want to be able to have a flag set for a specific entityID especially if that ID is something meaningful like an email or username like the docs mention.

I think this would be even less processing than a segment rule as there is not determining if an entity belongs to a segment or not since it is only determined by the entityID.

_FLI-671

[markphelps]

This is finally now supported with #2779 and the latest release https://github.com/flipt-io/flipt/releases/tag/v1.38.0 🎉