[fuzz] Add a ChannelDetails msg target

Author: TheBlueMatt

fuzz/src/bin/gen_target.sh

@@ -47,3 +47,5 @@ GEN_TEST msg_channel_update msg_targets::
 GEN_TEST msg_onion_hop_data msg_targets::
 GEN_TEST msg_ping msg_targets::
 GEN_TEST msg_pong msg_targets::
+
+GEN_TEST msg_channel_details msg_targets::

fuzz/src/msg_targets/gen_target.sh

@@ -45,3 +45,5 @@ GEN_TEST lightning::ln::msgs::ReplyChannelRange test_msg ""
 GEN_TEST lightning::ln::msgs::ErrorMessage test_msg_hole ", 32, 2"
 GEN_TEST lightning::ln::msgs::WarningMessage test_msg_hole ", 32, 2"
 GEN_TEST lightning::ln::msgs::ChannelUpdate test_msg_hole ", 108, 1"
+
+GEN_TEST lightning::ln::channelmanager::ChannelDetails test_msg_simple ""