release-23.1: tenantcapabilities: restructure interfaces

[blathers-crl]

Backport 1/1 commits from #100217 on behalf of @ajwerner.

/cc @cockroachdb/release

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This commit is mostly just a refactoring of what we have. The previous iteration had some unfortunate coupling between the protobufs and the top-level package. Having the protobuf generated code not be a leaf hurts.

Another pain point was the lack of strong typing when interacting with capabilities. Given this is go, somewhere there's a need to do some type assertion when dealing sets of variant instance types.

The biggest change is that the TenantCapabilities concept is no longer wrapped in an interface implemented by the protobuf. Instead, the Capability implementations now live inside the tenantcapabilities package, and can be looked up with FromName and FromID, without any access to concrete capabilities. These capabilies then know how to look up values in a strongly typed way from the concrete capabilities.

Epic: none

Release note: None

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Release justification: simplifies the code and ensures further backports are successful

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[ajwerner]

Will add #100294 before merging

[knz]

#100294 is merged

[knz]

I merged #100294 into this manually and will merge this PR once CI is green.