gitlab-ci: Enable gitlab page for publishing documentation

While adding pages, remove CI_JOB_ID and CI_JOB_SHA from PREFIX, as this
apparently is not needed. Make build-native-meson a dependency for the
pages stage.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
2 jobs for libweston-doc-breathe in 1 minute and 46 seconds
latest
Status Job ID Name Coverage
  Container Prep
passed #380722
container_prep

00:00:22

 
  Build
passed #380723
build-native-meson

00:01:23