A NegotiatedSerializer is passed into the API installer (and
ParameterCodec, which abstracts conversion of query params) that can be
used to negotiate client/server request/response serialization. All
error paths are now negotiation aware, and are at least minimally
version aware.

Watch is specially coded to only allow application/json - a follow up
change will convert it to use negotiation.

Ensure the swagger scheme will include supported serializations - this
now includes application/yaml as a negotiated option.