Create GHA to add issues and PRs to main board

### Overview

Since this is a non-primary repo under peopledepot, we want to manage its issues and PRs on the PD project board rather than create a new project for it. The project's workflow automation works with only one repo. This means we need a GitHub Action to add this repo's issues and PRs to that project.

### Action Items

- [ ] create GHA in this repo
- [ ] document it here and in peopledepot mkdocs

### Resources/Instructions

- Fang created an action after breaking PD project board's workflow for PRs. It needs cleanup but should work for this.
- peopledepot board is `https://github.com/orgs/hackforla/projects/61`, where
- orgName is `hackforla`
- projectNumber is `61`.