Allow non-Jira sources for SwitchBranches

[peasee]

In our release process with knope, we run a PrepareRelease step and raise the release changes on a PR for the rest of the team to review.

As part of our workflow file we manually checkout a branch like so before committing:

[[workflows.steps]]
type = "Command"
command = "git switch -C knope-release"

...

[[workflows.steps]]
type = "Command"
command = "git add ."

At the end of the workflow, once pushed, we delete the local branch so a user can re-run a release next time without a branch conflict because they're the same name.

I saw in the steps reference, there's a SwitchBranches but it seems to only support changing to a branch based on a Jira issue title/name/ID. It would be cool if we could:

1. Use another source into this step, like a variable to target a custom branch without needing Jira
2. Have some way to tell SwitchBranches to generate a branch ID for us, to make unique release branches. Perhaps SwitchBranches always generates a short UID and passes it as a variable, so we can make our custom branch name like release-$UID or however we'd like.

I think point 2 might be more controversial, but for us it would make sense to have something like release-abcdefg because we run a monorepo with many versions so it wouldn't make sense to have a release/0.0.1 branch. The unique ID would help avoiding local branch conflicts.

What do you think of this feature?