This implements the Imperative API that is served at /ext with Steve. The imperative API is compatible with Kubernetes' API server and will be used as an extension API server.
The header defined in RFC 9110[1] is "Accept", not "Accepts". This
change corrects the route filter. Since this API is not documented and
the header was plainly incorrect, no attempt is made at backwards
compatibility.
[1] https://www.rfc-editor.org/rfc/rfc9110.html#name-accept