Added --allow-experimental and --allow-beta CLI flags

[Rohan-flutterint]

• Added --allow-experimental and --allow-beta CLI flags and wired them into service startup so unstable components are only loaded when explicitly requested
• Introduced gating in the component environment to block beta/experimental plugins unless they are enabled, with opt-ins available via AllowExperimental/AllowBeta and stream-builder options for programmatic control
• Updated manager creation to respect the environment gating by constructing metrics and tracers through the global environment
• Closes : Experimental / beta components should require user to 'opt in'. #426

[joeblew999]

Great idea !!

[jem-davies]

@rohankumardubey - thanks for the effort with such a quick PR again 🚀

I had raised this as an issue because it's bad that the only thing to warn users regarding beta/experimental components are the warnings on the doc site - and that it would be cool if we had something like feature-gates from kubernetes.

The problem with fixing this, is that we will inevitably break the public API, and therefore to maintain semantic versioning, we would need to release it on a Major version update. Also prior to that we will need to review the state of experimental & beta components.

Maybe we could alter such that we log warnings for now, on a minor release, and mark this for a major release?

[jem-davies]

Going to pick this up and alter such that we emit warnings for now

[jem-davies]

OK so with #507 - we can flag the warnings (and in future potential terminal errors) at the time we Lint the configuration - meaning that we won't instantiate any components before shutting down. i.e. Catching the experimental / beta component earlier than the approach used here.