lnrpc: Clarify payment_addr and payment_secret

Fix #7438, adding clarification statements in lnrpc proto files.
Originally proposed by daredevil3435 in PR #7873 and PR #7885.

lnrpc/routerrpc/router.pb.go

@@ -480,6 +480,7 @@ type SendPaymentRequest struct {
 	// any channel may be used.
 	OutgoingChanIds []uint64 `protobuf:"varint,19,rep,packed,name=outgoing_chan_ids,json=outgoingChanIds,proto3" json:"outgoing_chan_ids,omitempty"`
 	// An optional payment addr to be included within the last hop of the route.
+	// This is also called payment secret in specifications (e.g. BOLT 11).
 	PaymentAddr []byte `protobuf:"bytes,20,opt,name=payment_addr,json=paymentAddr,proto3" json:"payment_addr,omitempty"`
 	// The largest payment split that should be attempted when making a payment if
 	// splitting is necessary. Setting this value will effectively cause lnd to
@@ -2099,6 +2100,7 @@ type BuildRouteRequest struct {
 	// pubkey.
 	HopPubkeys [][]byte `protobuf:"bytes,4,rep,name=hop_pubkeys,json=hopPubkeys,proto3" json:"hop_pubkeys,omitempty"`
 	// An optional payment addr to be included within the last hop of the route.
+	// This is also called payment secret in specifications (e.g. BOLT 11).
 	PaymentAddr []byte `protobuf:"bytes,5,opt,name=payment_addr,json=paymentAddr,proto3" json:"payment_addr,omitempty"`
 }
 

lnrpc/routerrpc/router.proto

@@ -306,7 +306,10 @@ message SendPaymentRequest {
     */
     repeated uint64 outgoing_chan_ids = 19;
 
-    // An optional payment addr to be included within the last hop of the route.
+    /*
+    An optional payment addr to be included within the last hop of the route.
+    This is also called payment secret in specifications (e.g. BOLT 11).
+    */
     bytes payment_addr = 20;
 
     /*
@@ -659,7 +662,10 @@ message BuildRouteRequest {
     */
     repeated bytes hop_pubkeys = 4;
 
-    // An optional payment addr to be included within the last hop of the route.
+    /*
+    An optional payment addr to be included within the last hop of the route.
+    This is also called payment secret in specifications (e.g. BOLT 11).
+    */
     bytes payment_addr = 5;
 }
 

lnrpc/routerrpc/router.swagger.json

@@ -927,7 +927,7 @@
         "payment_addr": {
           "type": "string",
           "format": "byte",
-          "description": "A unique, random identifier used to authenticate the sender as the intended\npayer of a multi-path payment. The payment_addr must be the same for all\nsubpayments, and match the payment_addr provided in the receiver's invoice.\nThe same payment_addr must be used on all subpayments."
+          "description": "A unique, random identifier used to authenticate the sender as the intended\npayer of a multi-path payment. The payment_addr must be the same for all\nsubpayments, and match the payment_addr provided in the receiver's invoice.\nThe same payment_addr must be used on all subpayments. This is also called\npayment secret in specifications (e.g. BOLT 11)."
         },
         "total_amt_msat": {
           "type": "string",
@@ -1173,7 +1173,7 @@
         "payment_addr": {
           "type": "string",
           "format": "byte",
-          "description": "An optional payment addr to be included within the last hop of the route."
+          "description": "An optional payment addr to be included within the last hop of the route.\nThis is also called payment secret in specifications (e.g. BOLT 11)."
         }
       }
     },
@@ -1774,7 +1774,7 @@
         "payment_addr": {
           "type": "string",
           "format": "byte",
-          "description": "An optional payment addr to be included within the last hop of the route."
+          "description": "An optional payment addr to be included within the last hop of the route.\nThis is also called payment secret in specifications (e.g. BOLT 11)."
         },
         "max_shard_size_msat": {
           "type": "string",