Feature request: Add flag to link created pull request with a GitHub project

[bxker]

The feature request

• Add an optional flag --gh-project-id to the multi-gitter CLI that adds an opened pull request to an existing GitHub project.

1. Use the PR id and the passed in project id to create the link, using this graphql mutation:

   mutation {
   addProjectV2ItemById(input: {
   projectId: "<GH_PROJECT_ID>"
   contentId: "<GH_PR_ID>"
   }) {
   clientMutationId
   }
   }

My use case I want to automate PR openings using multi-gitter and have them automatically be linked to a specified project.

Implementation

• [x] I would like to contribute this feature if it's a suitable addition to multi-gitter
• [ ] I have no intention of adding this feature myself.

[lindell]

This makes sense to add. I assume this is not available through the REST API? I could at least not find it with a quick search. The GraphQL API is already used for a few things, but not for any mutation.