Support linking of partners to projects

[AkshayGuptaK]

Is your feature request related to a problem? Please describe.
Currently, there is no support for linking project partners to the project they sponsor.

Describe the solution you'd like
In the project edit/create page, there should be a section by which admins can assign a partner for a project for a given time period, and edit/remove the existing partner assignments.

Additional context
A change log for the linked partners should also be stored in the database.

[bshankar]

Can we close this issue? This is solved by #6479.