Add an error proto to be returned by snuba RPc

proto/sentry_protos/snuba/v1/error.proto

@@ -0,0 +1,16 @@
+syntax = "proto3";
+
+package sentry_protos.snuba.v1;
+
+import "google/protobuf/any.proto";
+
+message Error {
+  // The HTTP status code corresponding to this error
+  int32 code = 1;
+
+  // The developer-facing message
+  string message = 2;
+
+  // Additional error information
+  repeated google.protobuf.Any details = 3;
+}