Add server support discovery endpoint

[zecakeh]

As per MSC1929.

Fixes #58.

Preview: https://pr1733--matrix-spec-previews.netlify.app

[turt2live]

generally this looks good to me - I have a bunch of minor editorial comments.

Thank you!

[turt2live]

We should define "administrator" somewhere here. I believe the MSC had some notion of what the admin's contact could be used for - can we incorporate that into the schema somewhere?

[zecakeh]

I don't see anything on the MSC about why the admins would be contacted, other than the description of the role property.

[richvdh]

I'm not convinced this belongs under "Server discovery". I'd be inclined to put it in a new "Module", but I'm open to other suggestions

[turt2live]

Rationale behind the suggestion to put it here is you're discovering information about the server without necessarily needing to speak the rest of Matrix. Both authenticated and unauthenticated clients can use this, and it's "before" the homeserver APIs really start to do anything.

Arguably though, we should rename or introduce a section for .well-known stuff. I think this is best left to a future PR at this stage.

[turt2live]

Thanks! Apologies for this taking so long to review.

If we do want to move it to another section/module, that can be done with a follow-up PR imo.

[richvdh]

It's a bit of an anomaly that https://spec.matrix.org/unstable/client-server-api/#well-known-uri now talks about "Servers hosting the .well-known JSON file", and now there are two .well-known JSON files. Generally I don't feel that section is particularly coherent now. But yes, we can improve this later.