Feat/replace old feature flags with flipper

[elasticspoon]

What github issue is this PR for, if any?

Resolves #XXXX

What changed, and why?

How is this tested? (please write tests!) 💖💪

Note: if you see a flake in your test build in github actions, please post in slack #casa "Flaky test: " :) 💪 Note: We love capybara tests! If you are writing both haml/js and ruby, please try to test your work with tests at every level including system tests like https://github.com/rubyforgood/casa/tree/main/spec/system

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