Add experiment assignment to Big Sky before plans

[paulopmt1]

Related to #99011

Proposed Changes

• We're adding the Big Sky before plans experiment
• Replaces the feature flag with a real Explat assignment 22179-explat-experiment
• Using the calypso_signup_onboarding_goals_first_bigsky_202501_v1 experiment
• Stop forcing the goals-first experience in development

It implements the first branch in this flow chart

p1738272885652059/1738193377.949839-slack-C085HCWCEDN

Why are these changes being made?

wpcalypso will continue to be forced onto the goals-first experience for stakeholders. But now that we have the new experiment slugs, developers should explicitly choose the cohorts they want to test with.

Testing Instructions

• In the Explat, configure your user to be in the treatment 22179-explat-experiment
• Go to the /setup/onboarding and make sure you can see Big Sky
• Finish the onboarding and make sure you're redirected to Big Sky

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 UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• 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-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-131741

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-131741&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-131741&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~709 bytes added 📈 [gzipped])

name               parsed_size           gzip_size
site-setup-wg           +870 B  (+0.2%)     +232 B  (+0.2%)
site-setup-flow         +870 B  (+0.2%)     +232 B  (+0.2%)
onboarding-flow         +826 B  (+0.4%)     +224 B  (+0.4%)
stepper-user-step       +823 B  (+0.3%)     +253 B  (+0.3%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[p-jackson]

I think we're assigning users to the experiment too soon. Checking about there here: p1738279560954329-slack-C7HH3V5AS

[p-jackson]

I think we're assigning users to the experiment too soon

The exposure event prevents bad things from happening 👍

[necronet]

ExPlat Approved