Add subcommand to update a cluster's subscription

[tomach]

Summary of the changes / Why this is an improvement

This adds a new subscommand to transfer a CrateDB cluster between subscriptions.

croud clusters subscription update \
  --cluster-id <cluster_uuid> \
  --old-subscription-id <old_subscription_uuid> \
  --new-subscription-id <new_subscription_uuid>

Checklist

• Link to issue this PR refers to (if applicable): https://github.com/crate/cloud/issues/2037

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

✨ Finishing touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch ta/transfer-subscription

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[plaharanne]

LGTM