Automatic merge from submit-queue (batch tested with PRs 44191, 44117, 44072)
[Federation] Cleanup e2e framework
This PR is intended to simplify maintenance of the federation e2e tests:
- refactor cluster helpers into framework so they can be reused by upgrade tests
- remove unused functions
- move backend pod management to the tests that require it rather than relying on the common cluster object
- use a slice instead of a map to manage cluster objects to make it simpler for tests that need it to find the primary cluster themselves
Commit ``fed: Refactor e2e cluster functions into framework for reuse`` was originally included in #43500, but is included here because it formed the basis for this cleanup.
cc: @kubernetes/sig-federation-pr-reviews @perotinus
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