Github integration

**Is your feature request related to a problem? Please describe.**
Most of the time when i push something to github using this tool i almost always browse to github after that to:
- create a MR
- react on a MR
- request a code review
- see if the CD/CI passes
- see if someone reacted on something

**Describe the solution you'd like**
Wouldn't it be nice if you could see the progress of a MR when i'm focused on a branch?
Or wouldn't it be nice if i can checkout code from a MR via lazygit.

**Describe alternatives you've considered**
Using the [github cli](https://cli.github.com/) but for this i still need to go outside of lazygit.

**Additional context**
Maybe it's possible to detect if the [github cli](https://cli.github.com/) is installed and if so use that to add these features to lazygit