Actions to author PRs for common usecases.

### TL;DR

The ergonomics of creating a PR with a properly formatted `iam.yaml` aren't great.

For common usecases, it would be nice to have a templated GH action that would author a PR for you (fill in project, resource, role, principal).

### Detailed design

```markdown
The main issue would be ensuring 2 party review was still enforced. GHTM can be used with GitHub script to author PRs (I believe we do this in abc-updater), but since the author is GHTM, someone could run the action and approve it themselves.

One solution would be to use the workflow we have been working on that enforces two users approving, and have people approve their as well as the actual reviewer.

There may be a more elegant solution, depending on if we can get information about who actuated the action when authoring the PR.
```

### Alternatives considered

```markdown

```

### Additional information

_No response_