new feature: autogenerate OBO pull requests

We currently generate both md and yml for obo metadata and purl requests, but it is up to the user to make a PR with these. We could easily have a script the user runs when they are happy to generate the PR

Start by tracing how the existing md and yml files for OBO metadata and purl requests are generated. Define the script's user-facing entry point and verify that, when the user is satisfied, it creates the intended pull request; the issue names no files or tests to run.

Written by the indexing model from the issue text.