Add namespace label toggle

What does this MR do?

This adds the functionality to change the namespace label when the GitLab managed checkbox is checked/unchecked on the cluster creation page.

The same functionality is added to the edit cluster screen.

Frontend for https://gitlab.com/gitlab-org/gitlab-ce/issues/52494

Preview

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides