Detecting spaces support

[dholms.xyz]

Just shipped this!

Atproto spaces alpha updates

A simple one today! No breaking changes, just two small things. We have a bigger release in the works probably for next Thursday. For today: Added a small temporary flag on describeServer for determining if you’re talking to a spaces-alpha compatible PDS (Impl / Forum Thread) Tightening up space repo lifecycle. In the code, specifically ensuring that the space exists before posting in a repo where the authorities are the same (Impl / Spec)