[Feature] Add I2p Crowdfunding Goal

**Description**: I noticed ZeroNet has a bunch of crowdfunding like goals for adding features like TOR. My request is to add one for adding I2p support.

_I don't want to be_ that person who just wants his feature added without recognizing the lots of things needed to get done but, I2p has been a popular request for a while and I think everybody can agree is greatly needed.

Plus any fundraising overflow can help raise fund other things too!

https://zeronet.io/docs/help_zeronet/donate/

Review the request and the linked ZeroNet donation page first; no implementation file or test is identified. Decide whether an I2P crowdfunding goal belongs on the donation page, define its scope and funding treatment, and confirm the expected result with maintainers.

索引モデルが issue の本文から書いたものです。