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

• [x] 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
• [x] A changelog entry has been made in the appropriate crates (if needed)