Submit and Review PRs

**Is your feature request related to a problem? Please describe.**
No, just would love not having to leave Lazygit. 😊

**Describe the solution you'd like**
I would like a method of reviewing and submitting PRs similar to the GitHub PR extension from Microsoft (link: https://github.com/microsoft/vscode-pull-request-github).

**Describe alternatives you've considered**
- Using the web interface
- Using GitHub desktop
- Using the VSCode extension (link again: https://github.com/microsoft/vscode-pull-request-github)
- Using GitHub CLI
- Using Graphite CLI (link: https://graphite.dev/)
* Note: Graphite doesn't *really* solve the issue because you can only create PRs, but being compatible with their stacked PRs would be nice if possible.

**Additional context**
I would like being able to do the following without leaving Lazygit:
- View a list of pending PRs
- Select a PR to review
- See the details of the PR (view diffs and any comments)
- Add general and/or line specific comments
- See reviewers needed and how many have reviewed
- See test status
- Create a PR

Possible steps:
- [ ] Setup GitHub auth
- [ ] Design rough layout (start with Lazygit layout
- [ ] Retrieve and display list of PRs
- [ ] Design rough PR details (diffs, general comments, button to approve)

Happy to help with this, but I realize it may not make since in Lazygit.