Investigate ways to consolidate automated PRs for deployments

[sjahl]

Right now, if you push multiple changes in quick succession to the master branch of the clinvar-submitter or genegraph, it's possible for PRs to pile up:

I'd like to look into methods for appending to an open PR if it already exists. A flow like this can be found here (via Github Actions) in the check-if-pr-already-exists job step in this blog post: https://sudolabs.com/blog/how-we-automatized-our-release-process-into-just-3-clicks