feat: Add multi-cluster management

[floreks]

Summary

• Add Create Cluster button to cluster overview
• Add create cluster modal
  • Block access for Open Source users
  • Support selection of Service Accounts without cluster and shell
  • Support creation of new Service Account if needed
• Update clusters list to properly display and give access to clusters that were not fully provisioned
• Update cluster picker to display cluster owner email (useful when there are multiple clusters with same name)
• Update ClustersContext logic to filter out "dead" clusters. In case the cluster is not CLI-based it will be checked for existing shell or installations.
• Update shell view and onboarding experience to properly support user impersonation
• Remove Create new cluster action from cluster picker on shell view
• and more... 🙂

Test Plan

Locally

Checklist

• If required, I have updated the Plural documentation accordingly.
• I have added tests to cover my changes.
• I have added a meaningful title and summary to convey the impact of this PR to a user.
• I have added relevant labels to this PR to help with categorization for release notes.

[github-actions]

Visit the preview URL for this PR (updated for commit f409033):

https://pluralsh--pr1153-create-multi-cluster-acfykhse.web.app

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