Tell project-config about itself

Due to the fact that we had to freeze config in order to filter
branch it as the seed repo for the creation of the project-config
repo, the patch that created project-config in config landed
after the filter branch. So the information about project-config
itself is not currently in project-config. This patch addresses
the situation.

Backport of: https://review.openstack.org/#/c/121650/15

Change-Id: I669fb70f2dabb57300e0e7cdddc49e16b7e67d47