Template support for Pull Request Description and Title

[klauern]

Describe the solution you'd like
When specifying the --pull-request-title and --pull-request-description it isn't clear to me that you can do anything other than copy or paste in a string of your choosing. It would be useful to allow a file to be specified, and beyond that, a template that can be given with prompts and/or options to enter variables to fill in the template for it.

Describe alternatives you've considered
I have a script to generate the git-xargs command runs, but it lacks some of the features that a multi-line description would offer, as well as just making it hard to parse the command.

Additional context