Please add subpaths support!

There are a lot of applications that require subpath support, Mastodon for simple example to support Streaming API. But, without support of subpath it's not possible to run it properly!

Moving upstream next to port would make it simplier to add multiple upstreams and also to add support for paths!

Another example where front/admin/api are running on 3 different ports. So, in case of SafeLine instead of using paths like /, /api, /admin we have to create 3 subdomains which is more that inconvenient. Imagine you have 20+ such of apps. That's like creating 60!!! applications in Safeline and managing them. Everyone will go nuts doing that!

Addedd in v9.3.1