Open PR from Project/Branches

[mbrevoort]

Is your feature request related to a problem? Please describe

As a user I want to be able to link to open a new Pull Request from the Project/Branches page, from the overflow menu. This plus #10168 would provide a complete workflow in the Gitpod UI when I need to do some work:

1. Create a new branch
2. Start a workspace
3. Make and test my change
4. Submit PR

Describe the behaviour you'd like

The menu should link to the corresponding PR creation UI if available based on which git integration the project is tied to. For example, the github URL would be: https://github.com/gitpod-io/gitpod/compare/{{BRANCH_NAME}}?expand=1

Describe alternatives you've considered

Go to github.com, hopefully see suggestion to create new PR from recent change, click the button. If I don't see the suggestion, navigate to the branch, find "Open Pull Request" under "Contribute" menu.

Additional context

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.