Automatically trigger GitLab Pages pipelines

Whenever master or one for the v9_* branches gets updated, the current
ARM should be published on GitLab Pages.  Add a pipeline stage which
takes care of triggering GitLab Pages pipelines.  Extend the lifetime of
artifact archives containing the ARM to prevent GitLab Pages pipelines
from failing due to artifacts being unavailable.

(cherry picked from commit 31bde118)
16 jobs for 565-automatically-trigger-gitlab-pages-pipelines-v9_11 in 25 minutes and 14 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Precheck
passed #70435
amd64 docker linux
precheck:debian:sid:amd64

00:00:21

 
  Build
passed #70436
amd64 docker linux
build:centos:centos6:amd64

00:02:29

passed #70437
amd64 docker linux
build:centos:centos7:amd64

00:02:40

passed #70438
amd64 docker linux
build:debian:sid:amd64

00:02:13

passed #70439
i386 docker linux
build:debian:sid:i386

00:01:58

 
  Test
passed #70440
amd64 docker linux
docs:debian:sid:amd64

00:00:52

passed #70449
amd64 docker linux
install:debian:sid:amd64

00:02:31

passed #70445
amd64 docker linux
systemtest:centos:centos6:amd64

00:04:23

passed #70446
amd64 docker linux
systemtest:centos:centos7:amd64

00:05:59

passed #70447
amd64 docker linux
systemtest:debian:sid:amd64

00:10:41

passed #70450
linux docker i386
systemtest:debian:sid:i386

00:10:29

passed #70441
amd64 docker linux
unittest:centos:centos6:amd64

00:01:05

passed #70442
amd64 docker linux
unittest:centos:centos7:amd64

00:01:04

passed #70443
amd64 docker linux
unittest:debian:sid:amd64

00:01:05

passed #70444
i386 docker linux
unittest:debian:sid:i386

00:00:55

failed #70448
i386 docker linux
systemtest:debian:sid:i386

00:11:14