feat: Add libp2p metrics

[bgins]

Description

This pull request adds the following features:

• Add libp2p swarm metrics
• Add metrics_record macro

Very much WIP. Depends on some initial work in #131.

Link to issue

Implements #184.

Type of change

• New feature (non-breaking change that adds functionality)
• Refactor (non-breaking change that updates existing functionality)

Test plan (required)

We will add integration tests to check the metrics.

[mxinden]

Unsolicited advice, this might be helpful: https://github.com/libp2p/rust-libp2p/tree/master/misc/metrics

[bgins]

Unsolicited advice, this might be helpful: https://github.com/libp2p/rust-libp2p/tree/master/misc/metrics

That looks great! Thank you for mentioning it. 🙏

[zeeshanlakhani]

Unsolicited advice, this might be helpful: https://github.com/libp2p/rust-libp2p/tree/master/misc/metrics

Yep. Well aware. We're not directly using the prom client lib, but this will be heavily influenced by that work y'all did :).

[bgins]

Closed because this branch is stale and not a priority at the moment. Leaving the issue open to pick up later.