Incorporates Kubernetes Namespace into Cluster's flow

What does this MR do?

Incorporates Clusters::KubernetesNamespace into clusters flow:

• Create the namespace/service account in GCP Kubernetes, when creating a cluster
• Create the namespace/service account in GCP Kubernetes, when adding a cluster
• Create the namespace/service account in GCP Kubernetes, when modifying namespace
• Replace KUBE_TOKEN and KUBECONFIG (passed to CI) with new credentials

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

Manual QA

ABAC Cluster

• Add a Cluster
• Check namespace/service account were created on kubernetes side
• Install applications
• Run AutoDevOps pipeline

RBAC Cluster

Creating cluster

• Create Cluster
• Check namespace/service account were created on kubernetes side
• Install applications
• Run AutoDevOps pipeline

Auto DevOps for ABAC

• Switch to master branch
• Create a cluster ABAC
• Switch to this branch, restart GDK
• Run Auto DevOps pipeline

Auto DevOps for RBAC

• Switch to master branch
• Create a cluster
• Switch to this branch, restart GDK
• Run Auto DevOps pipeline

.gitlab/issue_templates/Test plan.md

@@ -38,22 +38,22 @@ test plan](https://testing.googleblog.com/2011/09/10-minute-test-plan.html) and
 [this wiki page from an open-source tool that implements the ACC
 model](https://code.google.com/archive/p/test-analytics/wikis/AccExplained.wiki). -->
 
-|            | Simple | Secure | Responsive | Obvious | Stable |
-|------------|:------:|:------:|:----------:|:-------:|:------:|
-| Admin      |        |        |            |         |        |
-| Groups     |        |        |            |         |        |
-| Project    |        |        |            |         |        |
-| Repository |        |        |            |         |        |
-| Issues     |        |        |            |         |        |
-| MRs        |        |        |            |         |        |
-| CI/CD      |        |        |            |         |        |
-| Ops        |        |        |            |         |        |
-| Registry   |        |        |            |         |        |
-| Wiki       |        |        |            |         |        |
-| Snippets   |        |        |            |         |        |
-| Settings   |        |        |            |         |        |
-| Tracking   |        |        |            |         |        |
-| API        |        |        |            |         |        |
+|            | Secure | Responsive | Intuitive | Reliable |
+|------------|:------:|:----------:|:---------:|:--------:|
+| Admin      |        |            |           |          |
+| Groups     |        |            |           |          |
+| Project    |        |            |           |          |
+| Repository |        |            |           |          |
+| Issues     |        |            |           |          |
+| MRs        |        |            |           |          |
+| CI/CD      |        |            |           |          |
+| Ops        |        |            |           |          |
+| Registry   |        |            |           |          |
+| Wiki       |        |            |           |          |
+| Snippets   |        |            |           |          |
+| Settings   |        |            |           |          |
+| Tracking   |        |            |           |          |
+| API        |        |            |           |          |
 
 ## Capabilities
 
@@ -65,7 +65,7 @@ more complex features could involve multiple or even all.
 
 Example (from https://gitlab.com/gitlab-org/gitlab-ce/issues/50353):
 * Respository is
-  * Simple
+  * Intuitive
     * It's easy to select the desired file template
     * It doesn't require unnecessary actions to save the change
     * It's easy to undo the change after selecting a template
@@ -93,4 +93,4 @@ When adding new automated tests, please keep [testing levels](https://docs.gitla
 in mind.
 -->
 
-/label ~Quality
+/label ~Quality ~"test plan"
\ No newline at end of file