Successful runs on an integration branch should prune merged branches

[asmith-mdsol]

Using GitHub pull requests results in a large number of stale feature branches being left behind. CI runs should prune these merged branches automatically when appropriate.

[asmith-mdsol]

This is somewhat less useful now as GitHub supports delete branches in its UI but there may still be benefit in this for catching cases where people forget to do it themselves, or for those not using GitHub (or its UI).

[cross311]

I can see one danger in this: If you follow the git flow model the master branch is considered a merged branch. Also some teams use branches as their release tags, which would also be considered a merged branch.

[asmith-mdsol]

I think we'd make this opt-in and configurable if we added this.