clusters start: no-op when cluster isn't TERMINATED

[dkling-it]

Changes

databricks clusters start returns an API error if the target cluster isn't TERMINATED (e.g. it's already RUNNING). The command's own help text says otherwise: "If the cluster is not currently in a TERMINATED state, nothing will happen." This PR makes the command match that text: on INVALID_STATE, it prints a short message and exits 0 instead of failing.

Why

Fixes #1372. Scripts that call clusters start to make sure a cluster is up (a common idempotent pattern) currently have to special-case this error themselves. A previous attempt at this fix (#2947) took a similar approach but stalled and auto-closed without maintainer feedback.

Tests

Added cmd/workspace/clusters/overrides_test.go, covering:

• INVALID_STATE is swallowed and the command returns nil
• any other error still propagates unchanged

go build ./cmd/workspace/clusters/... and go vet ./cmd/workspace/clusters/... pass. I don't have a Databricks workspace to run this against a live already-running cluster, so I'd appreciate a maintainer or CI check on that path.

[github-actions]

Waiting for approval

Based on git history, these people are best suited to review:

• @janniklasrose -- recent work in .nextchanges/cli/, cmd/workspace/clusters/

Eligible reviewers: @andrewnester, @anton-107, @denik, @lennartkats-db, @pietern, @rclarey, @renaudhartert-db, @rugpanov, @shreyas-goenka, @simonfaltum

_{Suggestions based on git history. See OWNERS for ownership rules.}

[github-actions]

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• PR number: 6344
• Commit SHA: 44308703c617e6d4cad60b2b4f6953a73b71b8cb

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[dkling-it]

@janniklasrose the reviewer bot pointed at you for cmd/workspace/clusters/. This is a small one: clusters start returns an API error when the cluster is already RUNNING, which contradicts its own help text, so this swallows INVALID_STATE and exits 0. Checks are green. Any chance of a look, or is someone else better placed?