Add way to request reviewer state

### Describe the problem

Currently the reviewers need to get in touch with the project directly. It would be great to have a way in Weblate to require this status.

### Solution brainstorm

Something similar to requesting a new language as outlined in https://github.com/WeblateOrg/weblate/issues/20870.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

We want to avoid dealing this externally like https://github.com/WeblateOrg/language-data/issues/2552

Start by reviewing issue 20870 for the proposed request flow and issue 2552 for the external reviewer-state process this should replace. Done means Weblate can let users request and track reviewer state without handling the process externally.

Written by the indexing model from the issue text.