[website] Add blog post about Avalanche Post-Consensus

Summary: Explains why different types of user (exchanges, miners) should care

Test Plan: Ran it locally, read it and tested the links

Reviewers: #bitcoin_abc, bytesofman, Klakurka

Reviewed By: #bitcoin_abc, bytesofman, Klakurka

Subscribers: aimal, Klakurka, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D12088