Pattern Assembler - Enable feature flag pattern-assembler/write-flow in Horizon

[miksansegundo]

Proposed Changes

• Enable feature flag pattern-assembler/write-flow in the Horizon environment

This flag is already enabled for testing in wpcalypso env, but the issue with the LaunchPad Save modal is not reproducible there.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?

Related to #72565

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:commit-186561f3ca1866d0a1986bc752db875d1d83d6ee

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:commit-186561f3ca1866d0a1986bc752db875d1d83d6ee&env=jetpack

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[autumnfjeld]

Looks good to me! :) I'll update the CfT once you merge this. And then I'll test on horizon and we can see what's happening with the modal p1675847329299309/1675837107.374969-slack-CRWCHQGUB.