Update KB article docker-registry gitlab integration

[m-si]

Just stumbling upon the installation and found some minor quirks of the documentation, so I thought I leave my findings here for others:

1. the documentation says "chown -R cloudron:cloudron /media/registry-shared/" you are able to use user "yellowtent" if you don´t have user cloudron available (@girish or is this a security fail).
2. the documentation says

production:
  <<: *base

  registry:
    enabled: true
    host: <DOCKER_REGISTRY_HOST>
    ...

I found in my gitlab.yml "production: &base" and left it, like it was. When I did the change the KB article mentioned it didn't work out for me.

By the way is it possible to propose changes in the KB article like this, so the maintainers just have to accept (that might streamline the workflow a little and keep the KB articles faster up to date. Again thank you so much for your awesome work grish and johannes...really appreciating it.

[girish]

@m-si I guess you mean https://docs.cloudron.io/apps/docker-registry/#gitlab-integration ? That doc was contributed quite a while ago and I am guessing it has bugs as you found. Let me check and get back.

[m-si]

Exactly that was the article I was referring too. Beside oft my findings it worked for my installation like a charm.