feat(stackablectl): check for namespace before attempting uninstall

[sweb]

Description

Checks for default namespace before attempting to uninstall.

Output looks like this:

stackablectl -s stacks/stacks-v2.yaml -d demos/demos-v2.yaml demo uninstall trino-taxi-data
An unrecoverable error occurred: failed to execute demo (sub)command

Caused by these errors (recent errors listed first):
 1: demo "trino-taxi-data" cannot be uninstalled from the "default" namespace, because Kubernetes does not allow deleting it. Pass --namespace <NAMESPACE> if the demo was installed in a different namespace, or delete the demo's resources manually

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• CRD changes approved
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)

Reviewer

• Code contains useful comments
• (Integration-)Test cases added
• Documentation added or updated
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added

[xeniape]

LGTM just missing a changelog entry

[sweb]

LGTM just missing a changelog entry

@xeniape added changelog entry in cd1c493