Package GitLab Chart with Operator and ship it in the Docker image

the facility for rendering Helm Charts that is implemented in !9 (merged) assumes that the Chart and all of its dependencies are available on the file system. It does not attempt to locate and download the Chart from the Internet.

Therefore the designated GitLab Chart must be packaged with the Operator once the Docker image is built and ready to be shipped.

Ideally this is done automatically in the build pipeline, for example by passing the designated version of GitLab Chart as a CI variable and fetching the Chart and its dependencies with helm pull.

In order to do this a Docker image is needed (see #17 (closed)).