Document ESS endpoints

[leonhard-s]

OpenAPI is still primarily targeting REST APIs, and support for WebSocket or other streaming protocols seems an open issue that may never get first-class treatment.

A workaround for us would be to instead model these via a REST endpoint at push.planetside2.com/streaming, and faking the actual responses through POST/GET messages, with a big blinking "this is just a dummy" light flashing on top.

Alternatively, we could create and maintain a separate AsyncAPI spec that is able to model WebSocket subscriptions and messages correctly.

[leonhard-s]

This project is very close to what I envisioned: https://jhett12321.github.io/EventTrackerDocs/
Judging from the (now expired) domain, I believe this to be the (now archived) repository related to these docs: https://github.com/jhett12321/Planetside-2-Extended-Websocket-API

[leonhard-s]

A self-contained version of the WebSocket endpoint now lives in its own repository, including an HTML deployment via GitHub pages: https://github.com/leonhard-s/ps2-ess-api

Closing this issue as done; combining the two repositories is on the road map (