add support write only arguments for resources robot_account and user

[defimenko-ops]

Summary

• Add write-only credential arguments for harbor_user and harbor_robot_account.
• Implement rotation triggers with password_wo_version and secret_wo_version.
• Add validation rules, tests updates for the new workflow.

Details

• harbor_user:
  • add password_wo (write-only)
  • add password_wo_version
  • keep backward compatibility for password
  • add warning to prefer write-only alternative when possible
• harbor_robot_account:
  • add secret_wo (write-only)
  • add secret_wo_version
  • keep backward compatibility for secret
  • add warning to prefer write-only alternative when possible
• enforce schema constraints for valid combinations (RequiredWith/ConflictsWith)
• handle failed password/secret update paths without leaving stale values in state

Verification

• Unit tests:
  • go test ./provider ./client
• Acceptance tests (targeted):
  • TestAccUserWriteOnlyPassword
  • TestAccRobotProjectWriteOnlySecret
• Manual e2e check against Harbor in kind:
  • password_wo/secret_wo used successfully
  • cleartext secret values are not persisted in Terraform state

Closes #572

[defimenko-ops]

Hi, @flbla
Can someone review this change?

[flbla]

hi @defimenko-ops,
can you update the documentation ?

[defimenko-ops]

hi @defimenko-ops, can you update the documentation ?
@flbla
all ready!

[defimenko-ops]

Hi, @flbla !
What can I do to ensure my PR is approved?

[flbla]

hi @defimenko-ops,
please be patient, I do code reviews in my free time
it will be done, don't worry

[flbla]

LGTM