lnrpc: add create_missing_edge flag

lnrpc/lightning.proto

@@ -4558,6 +4558,15 @@ message PolicyUpdateRequest {
     // Optional inbound fee. If unset, the previously set value will be
     // retained [EXPERIMENTAL].
     InboundFee inbound_fee = 10;
+
+    // Under unknown circumstances a channel can exist with a missing edge in
+    // the graph database. This can cause an 'edge not found' error when calling
+    // `getchaninfo` and/or cause the default channel policy to be used during
+    // forwards. Setting this flag will recreate the edge if not found, allowing
+    // updating this channel policy and fixing the missing edge problem for this
+    // channel permanently. For fields not set in this command, the default
+    // policy will be created.
+    bool create_missing_edge = 11;
 }
 
 enum UpdateFailure {