cmd/lncli: add --peer flag to list channels

This commit adds a flag to listchannels that filters by remote pubkey.

lnrpc/rpc.proto

@@ -1385,6 +1385,12 @@ message ListChannelsRequest {
     bool inactive_only = 2;
     bool public_only = 3;
     bool private_only = 4;
+
+    /**
+    Filters the response for channels with a target peer's pubkey. If peer is
+    empty, all channels will be returned.
+    */
+    bytes peer = 5;
 }
 message ListChannelsResponse {
     /// The list of active channels

lnrpc/rpc.swagger.json

@@ -116,6 +116,14 @@
             "required": false,
             "type": "boolean",
             "format": "boolean"
+          },
+          {
+            "name": "peer",
+            "description": "*\nFilters the response for channels with a target peer's pubkey. If peer is\nempty, all channels will be returned.",
+            "in": "query",
+            "required": false,
+            "type": "string",
+            "format": "byte"
           }
         ],
         "tags": [