Fix for CI: Caching and [composer | webpack] does not exist

What does this MR do?

• added composer update in scripts/ci-backend-build → which should reduce the zip missing error
• added gitlab-runner in .gitpod.yml → for testing/working on the GitLab CI
• linted the .gitlab-ci.yml and added backend tests for deployment
• increased food basket duration time (test)

In Filesystem.php line 254:
                                                                               
  [RuntimeException]                                                           
  /builds/foodsharing-dev/foodsharing/vendor/behat does not exist and could n  
  ot be created.  

How confident are you it won't break things if deployed?

🤷