WIP: Automatically create service account/role restricted to only the project's namespace

What does this MR do?

Automatically create service account/role restricted to only the project's namespace and expose it as environment variable

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/51716

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Backend - To do

• Modify ServiceAccount to use project namespace
• Create a token for the new ServiceAccount
• If RBAC enabled create RoleBinding with edit access for the ServiceAccount
• If RBAC disabled, don’t create RoleBinding
• -Expose ServiceAccount as environment variable KUBE_SERVICE_ACCOUNT
• Replace KUBE_TOKEN with KUBECONFIG with new credentials

Refactor/Clean up

• Clarify CreateServiceAccountService specs
• Clean up constants on Clusters::GCP::Kubernetes
• Test for kubernetes variables
• Delete ClusterRoleBinding class?

Manual QA

• Create ABAC Cluster
• Install all applications on ABAC
• Create RBAC Cluster
• Install all applications on RBAC