Add documentation about Project Flare (hole punching, Circuit Relay v2, NAT traveral)

[BigLep]

Done Criteria

• Minimum: libp2p public docs doesn't contain any incorrect information about hole punching, circuit relay v2, NAT traversal, etc.
• Better: there is a way from libp2p public docs for a motivated reader to learn about the above.
• Best: a reader coming libp2p public docs gets a well organized presentation about how hole punching works in libp2p

Why Important

Hole punching is critical new functionality in libp2p. We need to help customers discover it and get roadsigns on how they can leverage it in their application.

User/Customer

Developers using libp2p in their application who would benefit from the expanded reach that hole-punching provides.

Notes

1. Given current resourcing, I don't expect us to get to "best". We can close without hitting it. I'd like to push for "better" because this should just mean providing links to some of the existing great documents we have about this effort.
2. Documentation sources that definitely should be review to at the minimum remove erroneous information are:
   1. https://docs.libp2p.io/concepts/circuit-relay/ (although maybe that was already done in content/concepts/circuit-relay: Update docs to v2 changes #112 ?)
   2. https://docs.libp2p.io/concepts/nat/
3. Even if we don't get to "best" level, we can still link to many resources that helps a motivated user learn more. This could include blog entires, public talks, spc, etc.

[BigLep]

I expanded the scope of this to be about project flare as a whole rather than just circuit relay v2.

[mxinden]

I would suggest copying most of https://blog.ipfs.io/2022-01-20-libp2p-hole-punching/.

[p-shahi]

As a quick win we can link to Max's blog post as well as the paper:
But we will eventually write it.