Enterprise Docker image isn't mentioned

[asachs01]

Context

For a number of folks who want to take advantage of GLE in Docker, we make no mention of GLE's Docker image, which makes the process of deploying GLE a bit of a PITA. For example, presently you'd have to download the docker image, then download each of the integrations plugins and mount those into Graylog. This is far from an ideal deployment scenario.

Expected Content

On https://docs.graylog.org/en/4.1/pages/installation/docker.html#here, we should note that there is an Enterprise image available which has all plugins baked into the image.