Automatically get Developers from connected Github repository

[skakim]

Is your feature request related to a problem? Please describe.
It is frustrating to give permissions to new collaborators from a Github repository manually to the related Infrabox project. New collaborators are also frustrated that they don't have the permissions they need when they need them, needing to ask someone to give them to him manually.

Describe the solution you'd like
Infrabox should use the Github hook to recover the list of collaborators in the Github repository and automatically give them Developer permissions in the related Infrabox project.

Of course, this being activated should be configurable in the project.

Describe alternatives you've considered

• Do manually, as it is done right now;
• Add a button "Add Collaborators from Github as Developers" that can be pressed by Admins instead of being fully automated;
• Add a button "Add me as Developer" that can be pressed by any logged-in user. Infrabox would check if the user is a collaborator in the Github project and, if yes, give him the Developer permissions.

Additional context
It would also be useful to give the Github Project's admins Admin permissions on the related Infrabox project, with a similar mechanism.