gitlab-ci: Use kaniko instead of docker-in-docker for image generation

kaniko can also work in unprivileged runners.

Based on v2 of
xorg/xserver!92 .
Acked-by: Alex Deucher <alexander.deucher@amd.com>
12 jobs for kaniko in 6 minutes and 27 seconds (queued for 42 seconds)
Status Job ID Name Coverage
  Docker Image
passed #68171
debian-testing

00:00:19

 
  Build
passed #68174
xserver-1.13

00:00:31

passed #68175
xserver-1.14

00:00:30

passed #68176
xserver-1.15

00:00:32

passed #68177
xserver-1.16

00:00:30

passed #68178
xserver-1.17

00:00:31

passed #68179
xserver-1.18

00:00:33

passed #68180
xserver-1.18-clang

00:00:35

passed #68181
xserver-1.19

00:00:31

passed #68182
xserver-1.19-clang

00:00:32

passed #68172
xserver-1.20

00:00:41

passed #68173
xserver-1.20-clang

00:00:36