Add multi site support to a bench

[Xieyt]

Description
Multi site support for a bench, where use a bench with multiple sites.

Expected Behavior
WIP

Current Behavior (if applicable)
User is only able to create a bench with only one site.

[dhsathiya]

One more use-case for this:

1. We require 11 containers per bench.
2. Keeping the number aside, the container spin up time is high. (Standard installation times)
3. Also, on MacOS, Docker containers consume a lot of resources.

When the requirement comes for spinning up a quick site for testing, that has 10+ apps, the standard setup time is high as we need to clone Apps, and then install them and then do the DB restore.

With this feature, the Apps will already be there, and a user just requires to do install-app. No need to setup everything from scratch.

[crelocks]

Do we have plans in the near future to enable this functionality?
One reason why I like frappe manager is that I can run this on arm64 instances.
I couldn't run frappe_docker repo on arm64 with multiple tenants (or at least I couldn't follow)