client_max_body_size setting via UI

[dreik]

Attempting to close ancient issue #914

Probably not the ideal solution, potential improvements are to follow nginx docs and allow this settings on both

1. server level
2. host level
3. location level

As of now it is only on host level

[nginxproxymanagerci]

Docker Image for build 4 is available on
DockerHub
as nginxproxymanager/nginx-proxy-manager-dev:pr-4217

Note: ensure you backup your NPM instance before testing this image! Especially if there are database changes
Note: this is a different docker image namespace than the official image