fix: add Gossipsub protocol to ALLOWED_PROTOCOLS in identify metrics

[Pronoss]

This PR addresses a TODO by adding the GOSSIPSUB_PROTOCOL_ID from libp2p_gossipsub to the ALLOWED_PROTOCOLS list used in the identify metrics module.

Previously, the Gossipsub protocol was commented out with a TODO placeholder. Now, it's conditionally included when the gossipsub feature is enabled, ensuring metrics can correctly account for Gossipsub-supporting peers.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates (if needed)

[Pronoss]

Hi @libp2p/rust-libp2p-maintainers – just a friendly reminder about PR #5992 (“fix: add Gossipsub protocol to ALLOWED_PROTOCOLS in identify metrics”). It conditionally includes GOSSIPSUB_PROTOCOL_ID when the gossipsub feature is enabled so our metrics correctly count Gossipsub peers. Whenever you have a moment to review, that would be awesome! Thanks! 🙏

[elenaf9]

This PR doesn't make any sense. GOSSIPSUB_PROTOCOL_ID doesn't exist.