Return unsupported labels when listing VPCs

[jeyhun]

Describe the problem/challenge you have
Currently, when one tries to list VPCs by passing labels selectors that are not supported, the following error message is returned:

unsupported label selector, supported labels are: [nephe.antrea.io/cpa-namespace nephe.antrea.io/cpa-name]

The error message does not state which label selector is not supported, so the developer has to check the source code to see where the List VPCs call was made and which label selectors were passed.

Describe the solution you'd like
The error message should state explicitly which label selector is unsupported, thus causing this error.

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment, or this will be closed in 90 days

[krishnamiriyala]

@jeyhun Is this still an issue?

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment, or this will be closed in 90 days