[Fixes] - Addressing test cases we found running sanity tests for Controller Plugin

[komer3]

The test cases to address:

• "should fail when requesting to create a volume with already existing name and different capacity"
  • We now throwing error with grpc code AlreadyExist when existing vol capacity differs from requested one.
• "should fail when the volume is already published but is incompatible"
  • Remove the capability for READONLY volumes since we do not support creating read only volumes on the cloud provider side at the moment. If needed, we could provide readonly capability on the Node Plugin side in future.

General:

• [ ] Have you removed all sensitive information, including but not limited to access keys and passwords?
• [ ] Have you checked to ensure there aren't other open or closed Pull Requests for the same bug/feature/question?

Pull Request Guidelines:

1. [ ] Does your submission pass tests?
2. [ ] Have you added tests?
3. [ ] Are you addressing a single feature in this PR?
4. [ ] Are your commits atomic, addressing one change per commit?
5. [ ] Are you following the conventions of the language?
6. [ ] Have you saved your large formatting changes for a different PR, so we can focus on your work?
7. [ ] Have you explained your rationale for why this feature is needed?
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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 36.38%. Comparing base (2a94023) to head (0cbd4a6). Report is 3 commits behind head on main.

Files	Patch %	Lines
internal/driver/controllerserver.go	0.00%	8 Missing :warning:
internal/driver/errors.go	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #198 +/- ## ========================================= + Coverage 0 36.38% +36.38% ========================================= Files 0 22 +22 Lines 0 1594 +1594 ========================================= + Hits 0 580 +580 - Misses 0 980 +980 - Partials 0 34 +34 ```

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