CA: Put APIs in a separate go module

[tenzen-y]

Which component are you using?:

ClusterAutoscaler

Is your feature request designed to solve a problem? If so describe the problem this feature should solve.:

If the external project imports cluster-autoscaler, the external project can't run go list -modfile=./go.mod -m all
because the cluster-autoscaler depends on k/k repository.

By these limitations, Goland (JetBrains) wouldn't work fine.
Please see the details: kubernetes-sigs/kueue#1345

Describe the solution you'd like.:

As we discussed in the above issue with @x13n and @alculquicondor, the best solution is to put APIs in a separate go module.

Describe any alternative solutions you've considered.:

Additional context.:

[tenzen-y]

/assign

[tenzen-y]

Probably, it would be better to put the client in a separate module as well.

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[tenzen-y]

/remove-lifecycle stale