Add changeset for Primitives + Theming Release

[wlee221]

Issue #, if available:

Description of changes: Adds changeset for primitives + theming release. Added a placeholder for now.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 524357e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@aws-amplify/ui-react	Major
@aws-amplify/ui	Major
@aws-amplify/ui-vue	Patch
@aws-amplify/ui-angular	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[ericclemmons]

I assume we'll make a final pass at the result in #596 ? Or what's the best place to editorialize & "collapse" them all into our first major release?

(I recognize that subsequent releases are best for changesets to communicate patches/minors)

[wlee221]

@ericclemmons Right, the final pass will be at #596. It's just that it's the best practice to add new changeset on its own PRs. #596 are just a consumer of changesets (you get to see what happens, but not modify) and are not meant to be editoralized.

I opened this PR because this "major" bump changeset will be at the top of the changelogs and is important enough to be its own PR.

[ericclemmons]

@dbanksdesign Since this will be top of the changelog, the bulk of it will be editorialized and likely cross-link to docs beyond summarizing what's in this.

[ericclemmons]

@dbanksdesign Can you add some content here that will headline our changelog?

I basically restated the goals & linked the RFC + docs:

https://github.com/aws-amplify/amplify-ui/pull/745/files

[slaymance]

🚢