Allow site renaming

Related: https://github.com/frappe/press/issues/725

The current process of migrating a site from one bench to another:
1. Take backup
2. Create a new site on the new bench, different domain name cause old site is still active
3. Make sure everything is working on the new site and then drop the old one
4. Create a new site again in the new bench with the old domain name

Allowing site renaming can cut down time and these steps.

A button to migrate from one bench to another makes it way easier for the end user, but site renaming is easier to implement(since it's already implemented :stuck_out_tongue_winking_eye:, just enable it for us users) and also better as it avoids all the hassle of issues arising on the bench migration.

Read related issue #725 and locate the existing site-renaming implementation referenced in the issue. Determine how it is currently restricted and where the user-facing migration action is exposed. Done means users can rename a site during bench migration without recreating it under a temporary domain.

Written by the indexing model from the issue text.