Add nginx linting to GitHub Action CI before building docker container

**What's the problem you want solved?**
Ensure, that the docker configuration is valid, we need to lint it and don't build the docker container if its incorrect.

**Is there a solution you'd like to recommend?**
?

Start by inspecting the repository's GitHub Actions workflow and Docker configuration to find the container build step. Identify how nginx configuration can be linted before that step, then run the workflow with valid and invalid configuration; done means invalid nginx configuration stops the build.

Written by the indexing model from the issue text.