release-24.1: mixedversion: split cockroach addressing into services

[renatolabs]

Backport 1/1 commits from #123680 and 1/1 commits from #124199.

/cc @cockroachdb/release

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This commit introduces the notion of services to the mixedversion framework. Previously, callers would reference a server by a node in the cluster. However, we want to move to a direction where there might be multiple services running in the cluster (i.e., not only the system tenant, but application tenant(s) as well). The service abstraction allows callers to perform operations either on the service that is serving application requests or directly on the system tenant.

The framework exposes the test's "default service". This represents the service that is responsible for handling application requests in a test. For traditional, non-UA deployments, this is the system tenant as usual. For UA deployments (not yet implemented), this will point to a tenant service created during test setup.

This reorganization should have no observable behavioural change for tests. However, it lays the foundation on which UA deployments will be implemented in the framework.

Epic: none

Release note: None

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Release justification: test only changes.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
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  here).
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If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• 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. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
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Also, please add a brief release justification to the body of your PR to justify this
backport.

[blathers-crl]

Your pull request contains more than 1000 changes. It is strongly encouraged to split big PRs into smaller chunks.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[renatolabs]

Mixed-version tests pass on this branch.

[renatolabs]

TFTR!