cloudapi: expose upload status

Expose a more detailed job status result - specifically, include upload status
alongside image status. Expand openapi.yml accordingly and add an UploadStatus
field to the OSBuildJobResult struct. At the moment, only represent the
"success" and "failure" states of UploadStatus - to differentiate between
"pending" and "running" would involve significant design decisions and should be
addressed in a separate commit.

internal/worker/json.go

@@ -24,6 +24,7 @@ type OSBuildJobResult struct {
 	Success       bool            `json:"success"`
 	OSBuildOutput *osbuild.Result `json:"osbuild_output,omitempty"`
 	TargetErrors  []string        `json:"target_errors,omitempty"`
+	UploadStatus  string          `json:"upload_status"`
 }
 
 type KojiInitJob struct {