The database contains some tables that are effectively used for configuration.
This commit starts to expose these to the guix service, enabling the
configuration to be handled by the service.
* gnu/services/guix.scm (<guix-data-service-configuration>): Add
git-repositories and build-servers.
(guix-data-service-configuration-git-repositories,
guix-data-service-configuration-build-servers): New procedures.
(guix-data-service-shepherd-services): Add new shepherd service to setup the
database.
Change-Id: I519efd9157b60f18c7e80e3bdc92c0e3c5729334
acb256d458