Allow branch plans to use Linked Repositories

Problem Definition

Currently, the configuration of repositories in branch plans can be one of the following:

1. Override the plan's default repository
2. Use the plan's default

Option 1 allows us to actually select a different branch for the branch plan from the plan's default, but it creates a new separate repository setting, which cannot be a Linked Repository setting.

If we, for example, change the password or the user, we must change the configuration of the plan's default and all branches that override the configuration.

In option 2, we cannot select a branch and the same branch is used in all cases, preventing the branch plan from running code in different branches.

Suggested Solution

I suggest:

1. Allow branch plans to connect to Linked Repositories
2. Allow a different branch from the one configured in the Linked Repository to be selected (requested here)

This way, we can use the same configuration, by overriding, but still only need to manage one.