- This enables us to use a scope to query all clusters in group
hierarchy order in one query, and also enables us to union to instance
clusters later.

- Handle case where clusters not present at level. In which case the
query should go ahead and return the next level's clusters.

- Swap with new CTE query behind Feature flag. This FF is default
disabled.

- JupyterHub must not be available (installed or updated)

- enabled uninstallation
- give it a specific uninstall message
- ajust specs

This enables terminals for group and project level clusters.
Previously there was no way to determine which project (and
therefore kubernetes namespace) to connect to, moving this
logic onto Environment means the assoicated project can be
used to look up the correct namespace.

Enable JIT Kubernetes resource creation for project level clusters

See merge request gitlab-org/gitlab-ce!29515

Project-level clusters that made use of this legacy
behaviour have been migrated to unmanaged clusters,
so we are now free to remove this fallback.

Previously this behaviour was only available to group
and instance-level clusters, as some project clusters
relied on Kubernetes credentials being passed through
to the runner instead of having their resources managed
by GitLab (which is not available when using JIT). These
clusters have been migrated to unmanaged, so resources
can be created on demand for the remaining managed clusters.

Allow switching clusters between managed/unmanaged

Closes #60617

See merge request gitlab-org/gitlab-ce!29322

Migrate Kubernetes service integration templates to clusters

See merge request gitlab-org/gitlab-ce!28534