[harshrajdebug]

What this PR does / why we need it:

A TrainJob with an env var name containing =, or with resource requests above its limits, is admitted today. JobSet then fails to create its Jobs (JobCreationFailed event only), and the TrainJob never starts and gets no condition. Details and the kind reproduction are in #4292.

This PR adds validatePodFields to the TrainJob validating webhook. It checks the env names and resource requirements the user sets directly:

• spec.trainer.env and spec.trainer.resourcesPerNode
• spec.initializer.dataset.env and spec.initializer.model.env
• env and resources of containers and init containers in spec.runtimePatches

Env names use validation.IsRelaxedEnvVarName, so only names that are invalid on every supported Kubernetes version are rejected. For resources, a request above the limit of the same resource is rejected; a request with no limit is still accepted.

On update the check runs only if the old object passes it, the same pattern used for the DRA feature gate fields. A TrainJob admitted before this check existed can still be suspended or have its patches changed, while an update that adds an invalid runtime patch is rejected.

The check does not look at values merged from the runtime template, for example a TrainJob request above a limit that only the runtime sets. That case needs the merged Pod spec and is left out of this change.

Tests:

• Unit: TestValidateCreate covers every field with an invalid value and checks the field paths, plus a case where requests equal limits or have no limit. TestValidateUpdate covers an update that adds an invalid patch and an update of an already-invalid TrainJob.
• Integration (test/integration/webhooks): trainer env A=B, requests above limits, and dataset initializer env A=B are rejected; valid names including my.config-1 and equal requests and limits are accepted. The three rejection entries fail on master.
• go test ./pkg/..., the webhook (92) and controller (54) integration suites, and golangci-lint run ./... pass locally.

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Fixes #4292

Checklist:

• Docs included if any changes are user facing

[google-oss-prow]

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