Add downgrade cancellation e2e tests

[henrybear327]

Part 2 of the e2e test - downgrade cancellation is called after the cluster has been partially downgraded (refer to part 1: #19244)

Reference: #17976

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.85%. Comparing base (35d20d1) to head (bffb8f9).
Report is 14 commits behind head on main.

Additional details and impacted files

see 35 files with indirect coverage changes

@@           Coverage Diff           @@
##             main   #19252   +/-   ##
=======================================
  Coverage   68.84%   68.85%           
=======================================
  Files         420      420           
  Lines       35689    35693    +4     
=======================================
+ Hits        24570    24575    +5     
- Misses       9693     9700    +7     
+ Partials     1426     1418    -8     

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[henrybear327]

/retest

[henrybear327]

Rebased to main as #19244 is merged

[henrybear327]

/retest

[ahrtr]

@siyuanfoundation PTAL, thx

[henrybear327]

While I was running e2e tests locally, the DowngradeCancel call times out (Error: etcdserver: request timed out) quite often, esp. with more nodes downgraded in the cluster.

Reference on CI: https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/etcd-io_etcd/19252/pull-etcd-e2e-amd64/1884558107229556736

[henrybear327]

/retest

[henrybear327]

I will look into pull-etcd-release-tests when all other tests have passed. This is probably not related to this PR.

[ahrtr]

I will look into pull-etcd-release-tests when all other tests have passed. This is probably not related to this PR.

kubernetes/test-infra#34236 should resolve the failure. It will be merged a couple of minutes later.

[k8s-ci-robot]

@henrybear327: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-etcd-release-tests	bffb8f9	link	false	/test pull-etcd-release-tests
pull-etcd-e2e-arm64	bffb8f9	link	true	/test pull-etcd-e2e-arm64
pull-etcd-e2e-amd64	bffb8f9	link	true	/test pull-etcd-e2e-amd64

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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