Signal `GossipQuery` support when using `IgnoringMessagHandler`

Signal `GossipQuery` support when using `IgnoringMessagHandler`

With its v24.02 release CLN made `GossipQueries` a required feature,
leading to a incompatibility between LDK and CLN when using
`IgnoringMessagHandler` as a `RoutingMessageHandler`, which is usually
the case when a node uses RGS.

To fix this issue, we let `IgnoringMessagHandler` signal `GossipQuery`
support, just to go ahead and ignore every gossip message the peer will
send us. While this is nonsensical and still might result in some
unnecessary bandwidth wasted, we have to do something to fix the
incompatibility.