GitHub importer - Send email to group owner after migration

When an import from GitHub is completed, we should send an email to Owner who initiated that mentions that the import is complete.

• To group owner(s), adding name of the person that triggered the import. So the copy would be "The import SOMeONE started on DATE from LINK_TO_HOST has completed. You can reassign contributions on the Group Members page."
• To the person who triggered the import, but tell them to contact the group owner to handle the contribution mapping. Copy would be "The import you started on DATE from LINK_TO_HOST has completed. Inform Group owner to reassign contributions on the Group Members page."

The email should look similar to the Direct Transfer email: