[Feature] Product-based release flow and scripts

[art-alexeyenko]

Part 3 of product-based release rework of the monorepo. The final goals of the initiative are to:

• be able to release products and packages separately and preserve the option to release all at once (the way it's done now)
• be able to track legacy (major - 1) versions of each product (nextjs, angular etc) to deliver hotfixes and minor updates when needed

The full plan is:

• Create separate template packages for product samples
• Update changesets to version 3
• Update Content SDK release scripts and GitHub Actions to include support for product releases and legacy product releases (this PR)

This current PR:

• Adds and enforces changeset split logic. In order to reliably pick changes to publish for a separate product release, we need separate changeset files. yarn changeset automatically splits the changeset. Additionally, PR action is added to do a breakdown during PR stage.
• Adds the 'Limited Release' action to prepare a product release, or a release for a single package. It prompts users to select packages for release, creates a separate branch and marks non-selected package to be ignored by changesets
• Adds a trigger for legacy branches creation. Legacy product branch is created when a major release is triggered for a product package. Legacy branch is a snapshot of repo at the time of previous major version.
  • Legacy branches are created for doing hotfixes for older versions easier
• Changes the 'Hotfix Prep' action to create release/hotfix/xyz branch (updated name)

[changeset-bot]

🦋 Changeset detected

Latest commit: ae3d188

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

This PR includes changesets to release 5 packages

Name	Type
create-content-sdk-app	Patch
@sitecore-content-sdk/nextjs	Minor
@sitecore-content-sdk/angular	Patch
@sitecore-content-sdk/content	Minor
@sitecore-content-sdk/react	Minor

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