lnrpc: use initiator enum for pending channel channel intiator

Update the PendingChannel message from a bool to an enum to
differentiate between the case where the remote party initiated the
channel and we have no record of the channel initiator. The previous
field has not been included in a release of lnd, so we can replace the
field directly.

lnrpc/rpc.proto

@@ -2093,8 +2093,8 @@ message PendingChannelsResponse {
         */
         int64 remote_chan_reserve_sat = 7;
 
-        // True if we initiated opening the channel.
-        bool initiator = 8;
+        // The party that initiated opening the channel.
+        Initiator initiator = 8;
 
         /// The commitment type used by this channel.
         CommitmentType commitment_type = 9;

lnrpc/rpc.swagger.json

@@ -1733,9 +1733,8 @@
           "description": "*\nThe minimum satoshis the other node is required to reserve in its\nbalance."
         },
         "initiator": {
-          "type": "boolean",
-          "format": "boolean",
-          "description": "True if we initiated opening the channel."
+          "$ref": "#/definitions/lnrpcInitiator",
+          "description": "The party that initiated opening the channel."
         },
         "commitment_type": {
           "$ref": "#/definitions/lnrpcCommitmentType",