Enhancement: Add feature to enforce unique reviewer approvals to required-review action when reviewer satisfies multiple 'all-of' teams

### Impacted plugin

None / Other

### What

I would like an option in the required-review github action to prevent a single reviewer from satisfying multiple teams within an 'all-of' block.

### How

From the current Readme: "When the key is all-of, a review is required from every team but if a person is a member of multiple teams, they can satisfy multiple requirements".

I'd like something like this:
`
- name: Conditional Additional Review
paths:
- 'some/other/pass/**'
teams:
- TeamC

- name: Standard 2 Required Reviews
paths:
- '**'
teams:
- unique-all-of:
- TeamA
- TeamB
`
'unique-all-of' would function exactly as 'all-of' currently does, except if a person is a member of both TeamA and TeamB, another reviewer would be required from either TeamA or TeamB.

Start with the required-review GitHub action and the README passage describing all-of. Trace where that configuration is interpreted, then verify the proposed unique-all-of example requires distinct reviewers across teams and document the option.

Written by the indexing model from the issue text.