Enable JIT Kubernetes resource creation for project level clusters

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

Since Kubernetes is creating the Secret and token asynchronously it is
necessary that we implement some delay or retrying logic to avoid a race
condition where we fetch a Secret before the token is even set. There
does not appear to be any way for us to force it to be set with any
synchronous API call so retrying seems to be the only option.

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.

- Split logger call for readibility
- Reduce code duplication by adding new method

This reflects how we now create or update

If the service fails mid-point, then we should be able to re-run this
service. So, detect presence of any previously created Kubernetes
resource and update or create accordingly.

Fix specs accordingly. In the case of finalize_creation_service_spec.rb,
I decided to stub out the async worker rather than maintaining
individual stubs for various kubeclient calls for that worker.

Also add test cases for group clusters

We remove configure_project_service_account and replace
ClusterPlatformConfigureWorker as they perform exactly the same piece of
work. This also makes GKE cluster creation to be the same as Adding
existing cluster - they both now use another worker to execute
CreateOrUpdateNamespaceService.