Updated Alpha / Beta Feature Test Coverage

[Benjamin Elder]

As previously mentioned, SIG Testing has been working this year to ensure alpha / beta features can be more easily tested. These jobs are now stable release signal, please help us keep them that way and leverage them to test your features.

Key CI jobs

"features" jobs that run alpha / beta e2e tests based on WithFeatureGate:

Testing Beta Features: kind-master-beta-features

Testing Alpha & Beta Features: kind-master-alpha-beta-features

"enabled" jobs to ensure that simply turning on alpha/beta features does not destabilize the cluster, these do run alpha/beta *tests*, they run stable tests:

Testing Conformance with Alpha & Beta *turned on*: kind-master-beta-enabled-conformance

Testing on-by-default tests with all Beta *enabled*: kind-master-beta-enabled

Testing on-by-default tests with all Alpha & Beta *enabled*: kind-master-alpha-beta-enabled

For each of these, if you see "ci-kubernetes-e2e-kind-alpha-beta-features" then there is an equivalent "pull-kubernetes-e2e-kind-alpha-beta-features" you can trigger on Pull Requests with a comment like this:

/test pull-kubernetes-e2e-kind-beta-features
/test pull-kubernetes-e2e-kind-alpha-beta-features

Tests must supply the featuregate to be included.

In the future we will find a home to document this and cross-link from the KEP testing guidance.
https://github.com/kubernetes/kubernetes/issues/131040
We will also revisit e.g. covering beta tests on Pull Requests by default. 

In the meantime, as the project stabilizes 1.35, please help ensure your new alpha/beta tests are passing reliably.

Thank you,
- Ben