- We're also improving specs to avoid this could happen again

Move generic k8s services out of GCP namespace

See merge request gitlab-org/gitlab-ce!32310

Feature flag has been defaulting to `true` since 12.2

Extract duplicated code from two similar classes into a parent one.

These services aren't specific to GCP, and will be used for AWS
as part of https://gitlab.com/gitlab-org/gitlab-ce/issues/46686

Kubernetes deployments on new clusters will now have
a separate namespace per project environment, instead
of sharing a single namespace for the project.

Behaviour of existing clusters is unchanged.

All new functionality is controlled by the
:kubernetes_namespace_per_environment feature flag,
which is safe to enable/disable at any time.

Also removes all logic from ClusterConfigureWorker
and ClusterProjectConfigureWorker, which are also
no longer used.

- Set as uninstallable app
- Update docs
- Adjust specs

Resolve "API support for group-level clusters"

Closes #55623

See merge request gitlab-org/gitlab-ce!30213

GitLab uses a kubernetes service account to perform deployments. For
serverless deployments to work as expected with externally created
clusters with their own knative installations (e.g. via Cloud Run), this
account requires additional permissions in the serving.knative.dev API
group.