* gnu/services/ci (<laminar-configuration>)[supplemental-groups]: New field. (laminar-shepherd-service): Exec laminard with supplementary groups. (laminar-account): Add supplementary groups to laminar user. * doc/guix.texi (Laminar): Document new configuration field. Change-Id: Iebfdbb58ea8c6dfa22bb8f64f6463e3ad133d2f9