Use authenticated user to search for existing comment (#40)

* feat: use authenticated user to search for existing comment

* ci: test with user PAT

* refactor: add username fallback case

* ci: revert to `GITHUB_TOKEN`

* refactor: remove unused `error` in try-catch

* build: run `npm audit fix`

* build: upgrade minor versions

* refactor: separate PR comment code from index file

* build: bump to version `1.5.2`

Author: phwt