feat: Optionally require S2S auth for the server /version endpoint

[jason-famedly]

Fixes: famedly/product-management (need a number)

Adds a new configuration setting possibility:

require_auth_for_server_version: false

true will mean no random people will be able to see what version a server is running without using a federation approved authentication. Defaults to false

A_26330 - Authentication of version queries
The Matrix Homeserver MUST authenticate outgoing requests to the /_matrix/federation/v1/version ¹ endpoint according to [Server-Server API/#request-authentication].

A_26331 - Rejection of unauthenticated version queries
The TI-M service MUST reject unauthenticated requests to the endpoint /_matrix/federation/v1/version ¹ with an HTTP 401 response.

Notes to consider: Famedly employees typically check that a server is online and responsive by checking this endpoint. This will no longer be viable. The client version of this end point is a potential work around. If a server endpoint is needed(due to workers or something) it may be possible to use the server keys endpoint instead

[itsoyou]

This looks good to me 💯, but 2 questions, do we need to align with other team about the version that contains this change?
and now we need to send authenticated requests, do we also need some change there? (I don't know where hehe)

[jason-famedly]

This looks good to me 💯, but 2 questions, do we need to align with other team about the version that contains this change? and now we need to send authenticated requests, do we also need some change there? (I don't know where hehe)

Aligning with other teams, I suppose not?
And for sending authenticated requests for this endpoint: Nope. Synapse does not need to make that request and so does not have the code to make it already in place 🤷‍♂️

This change was a request made by gematik, but with zero clear use cases beyond obfuscating exactly which version of the homeserver(and it's branding/model/etc) is currently being run. As such, this work is complete but seems rather unnecessary and will just sit here for a time on the back burner of the stove 😆