gitlab-ci: introduce main() in generating script

gitlab-ci: introduce main() in generating script

This script is currently very crude, but we're going to extend it, at
which point it will be nicer to have functions, local variables, et al.

Introduce a main() in preparation of those future evolutions.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>