feat: add nim peer

[gmelodie]

Adds peer that uses nim-libp2p

[dhuseby]

I just created a nim-peer-development branch for you to push into: https://github.com/libp2p/universal-connectivity/tree/nim-peer-development

I think you need to close this PR and create a new one. The way you do that is to provide the --base switch to specify the branch you want to push into:

gh pr create --base nim-peer-development

[gmelodie]

#308