add merge requests

[tsukinoko-kun]

Is your feature request related to a problem? Please describe.
I would like to use the familiar workflow of pull requests / merge requests in soft-serve.

Describe the solution you'd like
Add a command to create a merge request from one branch to another.
List open merge requests in the TUI with comments.
Approve and merge the request in the TUI.
Web hooks for all the events.

Describe alternatives you've considered
I considered writing another application that exists aside soft-serve to only do merge requests. I also considered not using the feature at all and moving the discussions and code reviews to another platform.

Additional context
I want to fully move away from GitHub with my company and private projects. I don't like the way alternative platforms like GitLab and Gitea work. soft-serve with it's TUI approach seems like a better solution.

If you have other suggestions on how to do code reviews outside of soft-serve, please let me know. The team is currently on Discord, but we will probably move to Slack or something else in the near future.

I am willing to implement this feature, but have little experience with bubbletea and no experience with wish.
I can also relate if you don't want a feature like this in the application.