Provide a config flag that allows the plugin to ship with beta features.

Users will then be able to activate and experiment with these features (at their own risk) on a dev Jenkins, using the main release of the plugin from the Update Center (without having to compile an experimental branch of the plugin from source as they do today).

This will also be helpful for exercising upcoming features where our test libraries cannot support us yet, e.g. for the upcoming cross-account secrets access feature while Moto doesn't support multiple accounts.

The support policy will be strictly best effort, no guarantees. The config schema within the beta section may change at any time without prior warning, and without readResolve() automatic config migration.

In CasC this would look like:

unclassified:
  aws....Provider:
    beta:
      someFeature:
        foo: "bar"
    endpointConfiguration:
      ... stuff
    filters:
      ... stuff

This would be mirrored with a 'beta' checkbox in the Web config UI.