Ignore mount path for git-credentials secrets and mount as file

[amisevsk]

What does this PR do?

Ignore any mount-path annotations on secrets labelled 'controller.devfile.io/git-credential'. Instead, always mount the merged git credentials secret to /.git-credentials/.

Additionally, mount the credentials file as files rather than using subpath mounts, in order to ensure changes to the on-cluster secret can be propagated to the running workspace without requiring a restart.

What issues does this PR fix or reference?

Closes #915

Is it tested? How?

1. Create a secret with git-credentials label:

   kind: Secret
   apiVersion: v1
   metadata:
     name: git-credentials-test-secret
     labels:
       controller.devfile.io/git-credential: 'true'
       controller.devfile.io/watch-secret: 'true'
   data:
     credentials: aGVsbG8gd29ybGQK # "hello world"
   type: Opaque

2. Start a workspace and verify file /.git-credentials/credentials is mounted and contains text "hello world"
3. Edit the secret in the cluster, changing the value of the credentials key
4. Update the workspace in any way to trigger a reconcile (e.g. add an annotation)
5. Check that file /.git-credentials/credentials reflects the new value (this may take some time to propagate down)

PR Checklist

• E2E tests pass (when PR is ready, comment /test v8-devworkspace-operator-e2e, v8-che-happy-path to trigger)
  • v8-devworkspace-operator-e2e: DevWorkspace e2e test
  • v8-che-happy-path: Happy path for verification integration with Che

[AObuchow]

Tested (following the PR instructions) and works as expected:

bash-5.1$ cd  /.git-credentials/
bash-5.1$ cat credentials 
hello world

Modified the secret credentials data to: fafghe9gd29ybGQK, added an annotation to the workspace, then:

bash-5.1$ cat credentials 
}����`world

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amisevsk, AObuchow, dkwon17

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[l0rd]

Should we update the documentation and remove the reference to controller.devfile.io/mount-path?