docker: Use a volume for backup configuration

Otherwise we need to rebuild the image. Thanks @duez.
See !877
7 jobs for feature-s/backup-container in 10 minutes (queued for 2 seconds)
Status Job ID Name Coverage
  Test Tools
passed #972161
test_tools

00:00:11

 
  Test Quality
failed #972162
allowed to fail
code_quality

00:00:05

 
  Test Unit
passed #972163
web
test_server_unit

00:00:21

 
  Deploy Review
passed #972164
deploy_review_server

00:00:37

passed #972165
manual
stop_deploy_review_server

00:01:22

 
  Test Functional
passed #972166
docker x86_64
ff32-server-functional

00:06:36

passed #972167
docker x86_64
ff45-server-functional

00:07:21

 
Name Stage Failure
failed
code_quality Test Quality
$ function propagate_env_vars() { # collapsed multi-line command
$ docker pull --quiet "$CODE_QUALITY_IMAGE"
unknown flag: --quiet
See 'docker pull --help'.
Uploading artifacts...
Runtime platform arch=386 os=linux pid=28690 revision=58272c27 version=12.7.0
WARNING: gl-code-quality-report.json: no matching files
ERROR: No files to upload
ERROR: Job failed: exit status 1