walletrpc: document that min conf_target is 2

Without this notice a developer might think that 1 is a valid value, which can
result in a rare bug. Example: lightninglabs/loop#898

Author: starius

lnrpc/walletrpc/walletkit.pb.go

@@ -841,6 +841,7 @@ message SendOutputsResponse {
 message EstimateFeeRequest {
     /*
     The number of confirmations to shoot for when estimating the fee.
+    Must be greater than 1.
     */
     int32 conf_target = 1;
 }
@@ -1396,6 +1397,7 @@ message FundPsbtRequest {
     oneof fees {
         /*
         The target number of blocks that the transaction should be confirmed in.
+        Must be greater than 1.
         */
         uint32 target_conf = 3;
 

lnrpc/walletrpc/walletkit.proto

@@ -325,7 +325,7 @@
         "parameters": [
           {
             "name": "conf_target",
-            "description": "The number of confirmations to shoot for when estimating the fee.",
+            "description": "The number of confirmations to shoot for when estimating the fee.\nMust be greater than 1.",
             "in": "path",
             "required": true,
             "type": "integer",
@@ -1577,7 +1577,7 @@
         "target_conf": {
           "type": "integer",
           "format": "int64",
-          "description": "The target number of blocks that the transaction should be confirmed in."
+          "description": "The target number of blocks that the transaction should be confirmed in.\nMust be greater than 1."
         },
         "sat_per_vbyte": {
           "type": "string",