Template support for Pull Request Description and Title

**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**