Branching process Julep

We need to figure out how we're going to handle branching going forward. For the immediate future we plan to keep `master` as 1.1, but we will need to figure out how we want to handle breaking changes in the long term.

The key questions
* How to structure our branches?
* What tooling can we use to minimise the need for manual intervention with handling backports?
* What should get backported to minor and patch releases?

Start by reviewing the three questions in the issue: branch structure, tooling for backports, and what belongs in minor and patch releases. Done means the project has an agreed long-term branching and backport policy; no files or tests are identified in the payload.

Written by the indexing model from the issue text.