Generate token for create-pull-request action using an app.

[ScottTodd]

This allows the created pull requests to run checks based on the pull_request trigger. See the documentation here:

• https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#triggering-further-workflow-runs
• https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#authenticating-with-github-app-generated-tokens

Sample PR: #390

[ScottTodd]

BTW @marbre we discussed assigning a github team as a reviewer. For now I did not grant this permission, but we can pretty easily add it if/when we want to do that.

Under Organization permissions: Members select Access: Read-only.
NOTE: Only needed if you would like add teams as reviewers to PRs.

https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#authenticating-with-github-app-generated-tokens