Move to per-component change logs

[WilliamKelley]

Problem

Avoids having to resolve changelog file conflicts between PR's.

Solution

Move to per-component changelogs. Keep the current paradigm of vNext (yyyy-mm-dd). Write a script that aggregates entries into a project-wide changelog on release. Write a script to auto-gen a changelog story from the entry.

[WilliamKelley]

To clarify, i would love to see the following, and for the aggregation script to be idempotent and it's output files (aggregate changelogs) should be able to be re-constructed if they were deleted.

/CHANGELOG.md

Aggregates of each library's (i.e. package's) changelogs.

OR, links to given changelogs.

libs/*/CHANGELOG.md

Aggregates of components' changelogs

libs/*/src/Component/CHANGELOG.md

Changelog of component. Sometimes Component is not a component, but a utility or set of utilities that has its own directory, e.g. ../src/theme/CHANGELOG.md.

Challenge: What happens if there's a change that needs to be stated at the project level? Like, "Drops support for React<=17"? It can't be inserted in the project's libs/*/CHANGELOG.md file since that must be able to be deleted. Maybe it lives in an analagous file like libs/*/VERSION_NOTES.md.

Additional notes

Each changelog should have a top level headerof it's name, second levels of versions, and dates and third levels of change categories . When a given changelog is aggregated, it's name (top-level header) should be associated somehow to all of it's corresponding notes. There are many ways to associated it, the current project's changelogs show one way, but I'm open to anything.

(# Component or # Project)
(## v1.0.0-alpha.1 (2022-01-01))
(### Features, Fixes, Breaking changes, or experimental/next)

--

Tree display if it helps

libs
├── spark
│   ├── ...
│   ├── src
│   │   ├── ...
│   │   └── Component
│   │       ├── ...
│   │       └── CHANGELOG.md
│   └── CHANGELOG.md
└── spark-icons
    ├── ...
    └── CHANGELOG.md
CHANGELOG.md

The spark-icons library won't have any changelogs below it's own. The files/components are all script-generated.