Add source field to debug information for better resolution informa…

…tion

authzed/api/v1/debug.proto

@@ -92,6 +92,11 @@ message CheckDebugTrace {
   // trace_id is a unique identifier for this trace. This identifier is only guanranteed
   // to be unique within the same overall Check or CheckBulk operation.
   string trace_id = 11;
+
+  // source holds the source of the result. It is of the form:
+  // `<sourcetype>:<sourceid>`, where sourcetype can be, among others:
+  // `spicedb`, `materialize`, etc.
+  string source = 12;
 }
 
 // CaveatEvalInfo holds information about a caveat expression that was evaluated.