api: swagger: review (JSON)stream response types

[thaJeztah]

    From the swagger, it looks like we have `BuildInfo`, `CreateImageInfo`, and `PushImageInfo`;

• None of those are referenced from within the swagger (this may be because those streams are not a good fit for Swagger, but I'd have to check why)
• It looks like all of them are effectively describing JSONMessage;

  moby/pkg/jsonmessage/jsonmessage.go

  Lines 135 to 151 in d73aba2

  	// JSONMessage defines a message struct. It describes
  	// the created time, where it from, status, ID of the
  	// message. It's used for docker events.
  	type JSONMessage struct {
  	Stream string `json:"stream,omitempty"`
  	Status string `json:"status,omitempty"`
  	Progress *JSONProgress `json:"progressDetail,omitempty"`
  	ProgressMessage string `json:"progress,omitempty"` // deprecated
  	ID string `json:"id,omitempty"`
  	From string `json:"from,omitempty"`
  	Time int64 `json:"time,omitempty"`
  	TimeNano int64 `json:"timeNano,omitempty"`
  	Error *JSONError `json:"errorDetail,omitempty"`
  	ErrorMessage string `json:"error,omitempty"` // deprecated
  	// Aux contains out-of-band data, such as digests for push signing and image id after building.
  	Aux *json.RawMessage `json:"aux,omitempty"`
  	}

We should have a look at those;

• If they're all describing JSONMessage, should they all be identical (or same type)?
• Possibly some endpoints don't use all fields, and due to the use of omitempty they are "different types" (from an API response perspective), although possibly that could be described with -x-nullable
• None of them describe the ProgressMessage (progress in JSON) and ErrorMessage (error in JSON) fields to be deprecated
• ProgressMessage appears to be marked as deprecated in 597e0e6 (Refactor stream #2945) - although no mention of the deprecation
• ErrorMessage was marked deprecated in 3043c26 (Do not require login unless 401 is received on push #1298) - need to check if there's actually still code using the field.

Originally posted by @thaJeztah in #44061 (comment)

[MDK8888]

Hey, I would love to work on this!