Add sections to the CHANGELOG

[steviez]

Add sections, such as CLI and validator, to CHANGELOG to introduce some grouping of items

Problem

There are several different types of "consumers" of the contents of the agave repo. These different consumers might care about different things (validators, developers, basic CLI users, etc), but the changelog currently has information for these different groups interleaved.

Summary of Changes

Introduce topic sections headers under reach release. Additionally, add headers for "Changes", "Breaking", "Deprecations" and whatever else may come up to reduce the indentations on the bullets

[steviez]

For now, I only did v2.2 section as a proof of concept / to gather feedback on. If folks like the format, I think I would proceed and update the previous releases to match the formatting.