Create merge commit if fast forward not possible when bidirectional mirroring

Bi-directional mirroring enables situations where branches me being modified on two different remotes. In some instances the branch can be fast forwarded. When this is not possible git can frequently automatically merge commit the changes and create a merge commit.

We should give users the ability to enable automatic merges when fast forward fails.

Proposal

• Add a new check box when bi-directional mirroring is enabled to allow merge commits

This depends on an improved interface, rather than simply enabling push/pull simultaneously on the same target.

Links / references

• #3745 (closed)

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

Who is this for? Provide one or more use cases.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml