Advertise route blinding feature as supported.

Now that we fully support forwarding blinded payments, we should advertise
support so nodes on the network can include us in their blinded paths.

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -9357,6 +9357,7 @@ pub fn provided_init_features(config: &UserConfig) -> InitFeatures {
 	features.set_channel_type_optional();
 	features.set_scid_privacy_optional();
 	features.set_zero_conf_optional();
+	features.set_route_blinding_optional();
 	if config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx {
 		features.set_anchors_zero_fee_htlc_tx_optional();
 	}

lightning/src/ln/peer_handler.rs

@@ -305,6 +305,7 @@ impl ChannelMessageHandler for ErroringMessageHandler {
 		features.set_channel_type_optional();
 		features.set_scid_privacy_optional();
 		features.set_zero_conf_optional();
+		features.set_route_blinding_optional();
 		features
 	}