BUG: fix issues creation in GH

[joecowton1]

We have an issue with issue creation, ironically.

Currently we use Alex's PAT, however since recent config changes mean this no longer works.

Akash has recommended we use a GH app instead - recently found https://github.com/github/combine-prs/blob/main/docs/github-app-setup.md to be a good guide on how to do this.