Support feature/development-branch specific packaging branches

[JMoerman]

Prerequisites

• [x] I have searched open and closed issues for duplicates.

Feature

Is your feature request related to a problem? Please describe.

Hi, I would like to have a way to have Houston CI deal with branches with dependencies that differ from the master branch. A solution was provided on medium, but unfortunately creating deb-packaging-branchname for a branch branchname doesn't accomplish anything, Houston will just pick the generic deb-packaging branch.

From https://medium.com/elementaryos/introducing-houston-ci-3179ec34e726:

Similarly, you can push packaging branches that match the naming of other branches for Houston CI. So if you have a feature branch called big-new-thing, you can create a matching packaging branch called deb-packaging-big-new-thing and Houston CI will test these branches together. This is especially handy if a feature branch introduces a new dependency. You can test a new, matching packaging branch and never introduce breaks in a CI-based workflow.

Describe the solution you'd like

I would like Houston to support branch specific packaging branches like described in the medium.com article. An alternative way of overriding the packaging configuration would also be fine.