InfluxDB 2.0: Creating instance of a proto dashboard should return "Not Found" for a Proto that doesn't exists [area/api]

[bednar]

The /protos/{protoID}/dashboards should return 404 HTTP response for a Proto that doesn't exists:

-> POST 
-> http://127.0.0.1:9999/api/v2/protos/020f755c3c082000/dashboards
-> {"orgID":"039ce622299e0000"}

<- 500 
<- Internal Server Error
<- {
	"code": "internal error",
	"message": "proto not found"
}

but currently the HTTP response is 500: Internal Server Error.