WebSocket URL may be redirected for stability reasons

[andypiper]

Per this conversation on Mastodon.

https://oisaur.com/@renchap/111739587756391314

I need to dig the WebSocket URL for streaming updates from the instance info because it's on a different hostname from the rest of the API, which the API docs don't mention as a possibility.

"This should be in the docs (and the "usual" endpoint should redirect to the new URL).
This is not specific to mastodon.social, a few "large" servers are using this feature to be able to have DDOS protection / CDN on the main domain with providers that do not support Websockets."

"which reminds me, the docs say the relevant URL is at Instance.configuration.urls.streaming_api https://docs.joinmastodon.org/entities/Instance/#streaming_api but I found it at Instance.urls.streaming_api on all the masto instances I'm testing on."

Relates to #1237