Status of configuration modifiers

[cbarrete]

There have been some questions on the unofficial Buck2 Discord chat about whether configuration modifiers are ready to be used or not.

My organization is interested in starting to use them, but it's unclear what their status is:

1. Are they considered somewhat usable/stable already, or do they still have an experimental/RFC status?
2. If they are already usable, would it be possible to add some documentation about them, even if minimal at first?

Thanks!