worker/osbuild: add host OS and architecture to job result

It is generally useful to have this information in the
`OSBuildJobResult`. This information is currently part of the
`OSBuildKojiJobResult`. Instead of moving it to the new
`KojiTargetResultOptions`, lets move it to the `OSBuildJobResult`
structure and set it for all jobs.

internal/worker/json.go

@@ -38,6 +38,10 @@ type OSBuildJobResult struct {
 	TargetErrors  []string               `json:"target_errors,omitempty"`
 	UploadStatus  string                 `json:"upload_status"`
 	PipelineNames *PipelineNames         `json:"pipeline_names,omitempty"`
+	// Host OS of the worker which handled the job
+	HostOS string `json:"host_os"`
+	// Architecture of the worker which handled the job
+	Arch string `json:"arch"`
 	JobResult
 }