.gitlab-ci.yml: use new jobs from the manifest repo

The .workspace and .build-docs allow simplification of the two
similar jobs present into this repository. The .workspace job
completely replaces the local copy, with a single configuration
variable to enable testing of incoming changes.

The build job becomes build-docs and extends both the .workspace job and
the .build-docs job, reusing both the scripts to perform everything that
was formerly specified explicitly.

The deploy job now extends the .workspace job but is otherwise
unchanged.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>
3 jobs for !164 with tweak/use-shared-jobs in 1 minute and 27 seconds (queued for 1 minute and 46 seconds)
detached
Status Job ID Name Coverage
  Compliance
passed #15334
dco

00:00:13

passed #15335
reuse

00:00:11

 
  Build
passed #15336
large-disk
build-docs

00:01:02