[Documentation Update]: Update contribution Q&A for stale PRs

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Description

Update [contribution Q&A](https://azure.github.io/Azure-Verified-Modules/contributing/q-and-a/) wiki page with guidelines on how to take over stale PRs from unresponsive authors

If
- the contribution is useful but would require updates
- PR authors are unresponsive to suggested comments

Then module owners are allowed to take over the PR
- merge author's branch to a newly created branch
- work on the codebase from there
- open a new PR. If the original PR was attached to an issue intending to close it, do the same with the new PR
- close the original PR with a comment referencing the new PR