Document how v2 feature flags will be used

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Why

In #520329 (comment 2567381213) we explored the idea of releasing in stages. In a follow up sync meeting, we realized that it is becoming harder to communicate about the possible release strategies and how the feature flags we have in mind will work together. We need to something to help in aid in discussing this.

What

• List any already existing v2 feature flags, and define their intended use for development and rolling out.
• List any potential v2 feature flags that we are considering, and what they would be used for.
• Add simple diagrams that can help in discussing these flags. It could show how they will be used in development and production. It could also show how v1 and v2 will interact or live side by side for a time.