Support workflow_call and allow branch selection / execution

[degrammer]

The GitHub Action renderer fails when a file contains a workflow_call property. It should be supported. This issue was reported via Discord

Note: It works, but order is important, if the yaml is not configured properly, e.g the workflow_call is after the workflow_dispatch it will fail, Runme could display a more useful error message for this situation.

Also, right now we support only the default branch, we need to explore adding support for different branches and even better, include a branch selector.

[admc]

Also make it possible to use something other than the main branch?