synadm support for Synapse over a Unix socket

[JacksonChen666]

Synapse supports listening over a Unix socket. The library synadm uses to make HTTP requests is requests (python) (pretty much the requests part of synadm), which doesn't appear to support Unix sockets (https://stackoverflow.com/questions/26964595/whats-the-correct-way-to-use-a-unix-domain-socket-in-requests-framework/#27268999), so synadm doesn't support Synapse installs which listen over a Unix socket.

• Synapse support: Search Unix socket support (Added in Synapse 1.89.0) in https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html#listeners
• Message asking about Unix sockets
• Possible solution (referenced library)

Some things to consider when implementing: The configurator (ask for http or unix, or try to interpret via some unix:// thing instead (handling URIs doesn't seem fun)), how synadm deals with library switeroo (and adding a dependency (plus distributions packaging synadm (although that might be a problem for distributions and not necessarily us)))

[JacksonChen666]

(Re: Feature/Core feature label: I'm not sure if this should be considered a core feature, and so just made it a normal feature label)

[JacksonChen666]

Another thing to consider is workers (which handle specific points sometimes e.g. media), but I'm not sure how that should be handled.