Remove image proxy setup instructions from Docker guide

[shyim]

We should stick to one solution for a problem :)

[Isengo1989]

We should not remove the whole context here and just link to another page. I would add a small section explaining what "Image Proxy" means, especially since this also aims at beginners.

Smth like : "An image proxy fetches production media files locally, avoiding CORS issues, reducing production load, and speeding up your local development environment."

As a second note, the original content explained the Image proxy with settings without shopware-cli—this adds a layer of complexity. We don't have shopware-cli as a Prerequisite set on the article. The question is, do we want that in an easy setup?