add feature flagging

[guergabo]

Describe the problem you are facing

Our primary api, the promise api, should be the only one exposed at this time imo. All other apis such as subscriptions should be hidden until they are ready for public consumption.

Describe the solution you'd like

I propose that we hide the experimental features behind feature flags. Users can enable the experimental features if they want, but they explicitly know not to expect a mature feature.

Looked at:

• https://prometheus.io/docs/prometheus/latest/feature_flags/
• https://gofeatureflag.org/docs
• https://github.com/open-feature

Alternatives you've considered

Another alternative would be to just document them as experimental/unfinished features. Although, we should prob do both.

Additional context

n/a

[favalos]

I will work on this.