Configure nginx client_max_body_size in Dockerfile

Configure the nginx client_max_body_size in the Dockerfile or docker-compose.yml file in order to make sure we no longer run into issues of deployments with maximum request sizes of 1 MB.

Set the value to 256 MB or some other sensible amount.

Whether it is possible to configure this setting in Docker, specifying and checking this setting should be added as a server setup step in README.md