Add branch support

The Pact Broker now supports branches as first class entities. You can read more about this here: https://github.com/pact-foundation/docs.pact.io/blob/feat/deployments-and-releases/website/blog/2021-07-04-why-we-are-getting-rid-of-tags.md

Please add support for branches in the following way (depending on how you publish pacts and verifications):

* If this