multi: let blinded path invoice options be set per addinvoice call

Extend the configurability of blinded paths in invoices by adding the
ability to change the global config options on a per-RPC basis.

lnrpc/invoicesrpc/invoices.swagger.json

@@ -395,6 +395,26 @@
         }
       }
     },
+    "lnrpcBlindedPathConfig": {
+      "type": "object",
+      "properties": {
+        "min_num_real_hops": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The minimum number of real hops to include in a blinded path. This doesn't\ninclude our node, so if the minimum is 1, then the path will contain at\nminimum our node along with an introduction node hop. If it is zero then\nthe shortest path will use our node as an introduction node."
+        },
+        "num_hops": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The number of hops to include in a blinded path. This doesn't include our\nnode, so if it is 1, then the path will contain our node along with an\nintroduction node or dummy node hop. If paths shorter than NumHops is\nfound, then they will be padded using dummy hops."
+        },
+        "max_num_paths": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The maximum number of blinded paths to select and add to an invoice."
+        }
+      }
+    },
     "lnrpcFeature": {
       "type": "object",
       "properties": {
@@ -579,8 +599,8 @@
           "description": "Maps a 32-byte hex-encoded set ID to the sub-invoice AMP state for the\ngiven set ID. This field is always populated for AMP invoices, and can be\nused along side LookupInvoice to obtain the HTLC information related to a\ngiven sub-invoice.\nNote: Output only, don't specify for creating an invoice.",
           "title": "[EXPERIMENTAL]:"
         },
-        "blind": {
-          "type": "boolean",
+        "blinded_path_config": {
+          "$ref": "#/definitions/lnrpcBlindedPathConfig",
           "description": "Signals that the invoice should include blinded paths to hide the true\nidentity of the recipient."
         }
       }