[NOUPSTREAM] Add GitLab CI support

Build a Kernel .deb package in GitLab CI and run a basic
LAVA boot test using Debian bookworm.

Co-developed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Co-developed-by: Sjoerd Simons <sjoerd@collabora.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>
Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>