[RFE] Configurable release branch pattern

[CermakM]

As a developer who wants to start using r-bot in an existing repo,
I want to be able to specify my own release branch naming pattern
so that I could stay consistent with the current naming conventions and
so that it is compatible with the current CI setup.

Example: My release branches are named release-{version}, but the bot implicitly creates {version}-release branch which is not compatible with my current CI setup.