lnrpc+rpcserver: allow abandonchannel to be used in regular build

An often requested feature is to use the abandonchannel API in regular
builds and not only dev builds to get rid of stuck channels that had
their funding transaction invalidated.
The initial reason for putting the call behind the build flag was a
safety concern to make sure nobody uses this on active channels by
accident.

lnrpc/rpc.proto

@@ -3363,6 +3363,13 @@ message AbandonChannelRequest {
     ChannelPoint channel_point = 1;
 
     bool pending_funding_shim_only = 2;
+
+    /*
+    Override the requirement for being in dev mode by setting this to true and
+    confirming the user knows what they are doing and this is a potential foot
+    gun to lose funds if used on active channels.
+    */
+    bool i_know_what_i_am_doing = 3;
 }
 
 message AbandonChannelResponse {

lnrpc/rpc.swagger.json

@@ -197,6 +197,14 @@
             "required": false,
             "type": "boolean",
             "format": "boolean"
+          },
+          {
+            "name": "i_know_what_i_am_doing",
+            "description": "Override the requirement for being in dev mode by setting this to true and\nconfirming the user knows what they are doing and this is a potential foot\ngun to lose funds if used on active channels.",
+            "in": "query",
+            "required": false,
+            "type": "boolean",
+            "format": "boolean"
           }
         ],
         "tags": [

rpcserver.go

@@ -2369,8 +2369,13 @@ func (r *rpcServer) AbandonChannel(_ context.Context,
 	// If this isn't the dev build, then we won't allow the RPC to be
 	// executed, as it's an advanced feature and won't be activated in
 	// regular production/release builds except for the explicit case of
-	// externally funded channels that are still pending.
-	if !in.PendingFundingShimOnly && !build.IsDevBuild() {
+	// externally funded channels that are still pending. Due to repeated
+	// requests, we also allow this requirement to be overwritten by a new
+	// flag that attests to the user knowing what they're doing and the risk
+	// associated with the command/RPC.
+	if !in.IKnowWhatIAmDoing && !in.PendingFundingShimOnly &&
+		!build.IsDevBuild() {
+
 		return nil, fmt.Errorf("AbandonChannel RPC call only " +
 			"available in dev builds")
 	}
@@ -2411,7 +2416,9 @@ func (r *rpcServer) AbandonChannel(_ context.Context,
 		// PSBT) on the channel so we don't need to use the thaw height.
 		isShimFunded := dbChan.ThawHeight > 0
 		isPendingShimFunded := isShimFunded && dbChan.IsPending
-		if in.PendingFundingShimOnly && !isPendingShimFunded {
+		if !in.IKnowWhatIAmDoing && in.PendingFundingShimOnly &&
+			!isPendingShimFunded {
+
 			return nil, fmt.Errorf("channel %v is not externally "+
 				"funded or not pending", chanPoint)
 		}