identify/handler: Improve property name

[elenaf9]

Description

Nit: Rename IdentifyHandler.next_id to IdentifyHandler.trigger_next_identify to better reflect what it is actually doing.

Throughout rust-libp2p, we use next_*id for identifiers (e.g. next_connection_id: ConnectionId).
IdentifyHandler.next_idis not an id, but instead a Delay that triggers the next outbound substream request, hence the old name is misleading.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• A changelog entry has been made in the appropriate crates
  • don't think a changelog entry is needed for this since it is only internally?

[thomaseizinger]

Thanks!

That is indeed a much better name :)

[mxinden]

👍 Thanks!