Implement controlled rollout of features based on teams

[roperzh]

Goal

We want to allow users to do canary rollouts for their features so that they can test it out for their install base before committing to a full rollout. This allows our users to validate scalability, usability, and impact of various features.

How?

Backend

• add a mechanism to deprecate AppConfig settings w/ backwards-compat #7353
• deprecate host_settings in favor of features #7358
• enable controlled rollout of features by teams #7408

Related

• Epic: Feature flags: Controlled rollout of Fleet features by team #6838