Add port checking
This pull request adds the ability to check if the CSM server is reachable from the outside. When starting the CSM server, a check request is sent to a server hosted by me to check for the open port. The result is displayed in the chat. To check the status again, use the Multiplayer Menu -> Manage Server menu.
The server implementation can be found at https://github.com/CitiesSkylinesMultiplayer/CSMChecker, which is currently running at https://csm-check.kaenganxt.dev.
Some dependencies were also updated.
Rust, nice!
Should we also maybe intergrate the version checker into this API as well? (see https://github.com/CitiesSkylinesMultiplayer/Website/pull/5/files for a mockup)
We can maybe cache the latest version (from https://api.github.com/repos/CitiesSkylinesMultiplayer/CSM/releases) and return it via /version or something.
Related to https://github.com/CitiesSkylinesMultiplayer/CSM/issues/271
I'll look into it!
All happy with this?