Transition service account controller clients to TokenRequest API

[enj]

The controller manager handles controller clients via the ControllerClientBuilder interface. The core implementation is SAControllerClientBuilder (see k8s.io/kubernetes/pkg/controller/client_builder.go). To get a client for a specific service account, it ensures that the service account exists, and then waits for the token controller to create a secret that contains the service account's token. While the long term desire may be to remove the token controller, we can work towards that goal by moving these clients to the TokenRequest API.

Action items:

1. Switch the controller manager clients to auto rotating tokens not persisted in secrets
2. SAControllerClientBuilder should check if the TokenRequest API is available and use it, otherwise it should fallback to the current behavior of using secret based tokens
3. Determine how to opt out of the token controller generated secrets (so that the only tokens for these controller clients are ephemeral and short lived)
4. Possibly clean up legacy tokens for the controller service accounts after a release

/sig auth
/sig api-machinery

@kubernetes/sig-auth-feature-requests

xref: #70679

[enj]

/assign

[WanLinghao]

/cc

[jennybuckley]

/cc @yliaog

[fejta-bot]

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[enj]

/reopen

Some aspects remain.

[k8s-ci-robot]

@enj: Reopened this issue.

In response to this:

/reopen

Some aspects remain.

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[enj]

/remove-lifecycle stale

[enj]

Opened #77599 and #77600 to cover the remaining work.