RFC to ensure that unstable components are opt-in only

[mx-psi]

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Components are clearly labeled with stability levels, which can be inspected via e.g. logs. However, it is currently too easy for unstable components to be used without realizing that they are unstable.

We want to make it so users have to explicitly think about using unstable components. To that end we discussed a few ideas:

• Make core (or a new distribution) that is focused on a core set of stable components (to be expanded/modified from the current list). Make this the 'official' distribution and make contrib less used
• Introduce a new --min-stability-level=<unknown|unmaintained|development|alpha|beta|stable> CLI flag/config field to the Collector binary (or, possibly, to OCB) that is gradually raised over time and that prevents usage at runtime of components below a minimum stability level. Raising the minimum stability level would have to happen in an informed way via, e.g., the Collector survey results or data from vendors.

This issue tracks the creation of an RFC that defines a holistic vision on how to do this. The final RFC probably would have to mix several of these (since, e.g. a component has per-signal stability levels but we currently cannot add only some signals from a component).

If the RFC talks about a new distribution/a redefined 'core' distribution, it does not need to define what specific components it includes (that can be an independent discussion).