API: 'listforwards' now include 'payment_hash' field

'payment_hash' can help users learn more about the forward payment.

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - plugins: a new boolean field can be added to a plugin manifest, `dynamic`. It allows a plugin to tell if it can be started or stopped "on-the-fly".
 - lightningd: check bitcoind version when setup topology and confirm the version not older than v0.15.0.
 - startup: space out reconnections on startup if we have more than 5 peers.
+- JSON API: `listforwards` includes the 'payment_hash' field.
 
 ### Deprecated
 

lightningd/peer_htlcs.c

@@ -2114,6 +2114,9 @@ static void listforwardings_add_forwardings(struct json_stream *response, struct
 		const struct forwarding *cur = &forwardings[i];
 		json_object_start(response, NULL);
 
+		json_add_hex(response, "payment_hash",
+			     cur->payment_hash,
+			     sizeof(*cur->payment_hash));
 		json_add_short_channel_id(response, "in_channel", &cur->channel_in);
 		json_add_short_channel_id(response, "out_channel", &cur->channel_out);
 		json_add_amount_msat_compat(response,