Basic mode option to rebase from remote branch

[isc-pbarton]

Use case is in trunk-based development, where a developer is working in a feature branch, but wants to regularly merge in changes from a different remote branch (e.g. production).

In Basic mode, add a step to the sync option: it should fetch, pull, merge from a remote branch, commit, then push. There should be a new setting that specifies which remote branch should be merged from.

[isc-pbarton]

If there is a merge conflict that makes it not possible to rebase the other remote branch, the user should be directed to resolve the conflict between the feature branch and the other remote branch on the remote.