update doc to reflect password secret behaviour

[anandrkskd]

What type of PR is this?

/kind documentation

What does this PR do / why we need it: This PR updates documentation for using argocd-cluster and argocd-secret secrets behavior.

Have you updated the necessary documentation?

• [ ] Documentation update is required by this PR.
• [X] Documentation has been updated.

Which issue(s) this PR fixes:

Fixes https://github.com/argoproj-labs/argocd-operator/issues/1483

How to test changes / Special notes to the reviewer:

[anandrkskd]

hey @svghadi, can you review this PR