[Tools] Implement Release channels

[whitneygriffith]

Part of #173

• Separate YAMLs are created for each release channel with its appropriate APIs and API versions
• Separate YAMLs are created for each release channel with its appropriate APIs and API versions
• CRDs in each channel has its appropriate storage and served versions

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• ✅ login: whitneygriffith / name: Whitney Griffith (8844238, a340947)

[whitneygriffith]

After taking into consideration our discussions around Legacy Channel. We have decided to only have two release channels, and rename them to avoid users thinking that the overall Istio Functionality has regressed.

With that being said, the Release Channels proposal has been updated to have the Standard Channel (Full Istio Functionality) and Stable Channel (GA Istio Functionality.

Standard Channel:

• Functionality Focus: The Standard Channel encompasses the entirety of Istio’s features, regardless of their current stage of development or stability.
• Inclusive of Experimental Features: Users opting for the Standard Channel gain access to all features offered by Istio, including those in the experimental stage. This allows for early adoption and testing of cutting-edge functionalities.
• Varied Stability Levels: Features in the Standard Channel may range from experimental to stable, providing a broad spectrum of capabilities to users who are willing to explore and experiment with the latest advancements.

Stable Channel:

• Stability Assurance: The Stable Channel is curated to include only the parts of Istio that have reached a stable, generally available (GA) state. This ensures reliability and consistency for production environments.
• GA Features Only: Users selecting the Stable Channel can expect to access features that have undergone thorough testing and validation, and are deemed suitable for use in mission-critical applications.
• Risk Mitigation: Opting for the Stable Channel minimizes the risk of encountering unexpected behavior or breaking changes, providing a dependable foundation for deploying Istio in production environments.

Please review the doc again and raise any comments.

[keithmattix]

@istio/wg-test-and-release-maintainers istio/api#3133 is incomplete until this change + the accompanying api and pilot PRs get merged. We also want to make sure Whitney has time ti prepare blog posts and docs for release channels before 1.22 is released so please take a look!

[whitneygriffith]

Do we want to keep the functionality of parsing the release channel annotations for CRD generation?

[keithmattix]

Maybe keep this around as a long-lived branch? I can see the functionality being picked up later and it would be better not to start from scratch