User profile: Add GitHub social link

# Problem
Similar to:
- https://github.com/Joystream/pioneer/issues/4540
A very common question from users researching projects will be to understand who the development team is--while we have some limited info on the main website it is far more attractive for developer GitHub profiles to be viewable on their Joystream profile within Pioneer such that a user can visit the Builders WG and see the GH accounts of active builders.
Obviously the UI could be improved to showcase this data better at a later point in time, but it would be good to have the option to link to GH profiles for the purpose of verification and research.

Start at the user profile entry point in Pioneer and review the related issue #4540 for an existing pattern. Trace how profile data is displayed and determine where a GitHub profile link belongs; done means users can view and follow a builder’s GitHub profile from their Pioneer profile.

Written by the indexing model from the issue text.