[discuss] Adopt common Service interface

[joshdover]

Summary

This PR demos adopting the Service interface and basing the Plugin interface on it as proposed in #47065 (comment)

Currently, this only demos a single Core service using this pattern. Open questions:

• Should we make stop required? It's currently optional for Plugin but required for CoreService
• Should we include this ServerType utility?
• Should we separate the Service type used by plugins vs. the CoreService type used by Core?

[skip-ci]

Checklist

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[elasticmachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request
• Commit: 04a9387

[joshdover]

@elastic/kibana-platform thoughts on the questions posed above?

[pgayvallet]

Should we make stop required? It's currently optional for Plugin but required for CoreService

For consistency's sake, I lean toward yes. Implementing an empty stop doesn't seems that bad in worse case scenario, and the fact that the method will always be present may helps developer about thinking that maybe they needs to put something in it.

Should we include this ServerType utility?

I'm personally against that kind of (imho way too magical) type inference. I think explicit typing makes more sense.

Should we separate the Service type used by plugins vs. the CoreService type used by Core?

I feels like that's probably 'safer'. I don't see any cons to distinguish them, and that's a safeguard if their interfaces needs to diverge at some point.