Gossipsub v2.0

[ppopth]

The gossipsub v2.0 is defined in the spec here https://github.com/libp2p/specs/pull/653.

I made this PR as a draft first because the spec is still a draft and to get some visibility.

I need to implement this early even if the spec is still in an early stage because I have to use it to do simulations.

• [x] Handling receiving messages and send out IANNOUNCE
• [x] Adding test cases for sending out IANNOUNCE
• [x] Handling IANNOUNCE and send out INEED
• [x] Adding test cases for handling IANNOUNCE and sending out INEED
• [x] Handling INEED and sending out the message
• [x] Adding test cases for handling INEED

Optional:

• [ ] Adding WithIgnoreIneed option to make it easier to create a malicious node that never replies to INEED

[ppopth]

I'm not sure if WithIgnoreIneed should be added to the upstream repo, but I will implement it in my local repo anyway because I need it for my simulations in malicious cases.