Add .gitlab-ci.yml

2 jobs for master
Name Stage Failure
failed
deploy-plugins Deploy
  File "/builds/gajim/gajim-plugins/.ci/deploy.py", line 145, in <module>
index = download_package_index()
File "/builds/gajim/gajim-plugins/.ci/deploy.py", line 64, in download_package_index
r.raise_for_status()
File "/home/worker/.local/lib/python3.9/site-packages/requests/models.py", line 960, in raise_for_status
raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: https://ftp.gajim.org/plugins/master/package_index.json
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1