Update experiment slug for goals-first experience

[p-jackson]

Related to #99011

Proposed Changes

• Switches to the new calypso_signup_onboarding_goals_first_flow_holdout_v2_20250131 experiment slug
• 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?

We are adjusting weightings for the goal-first experience. It's now 10% control and 90% with the goals-first experience. That 90% is split into holdout and cumulative cohorts, but that doesn't make any difference for the useGoalsFirstExperiment() hook. Both treatment cohorts get the goals-first experience.

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

• Use Explat to set the calypso_signup_onboarding_goals_first_flow_holdout_v2_20250131 experiment to your desired cohort 22180-explat-experiment
• Clear your local storage and visit /setup/onboarding
  • control sees the domains step (or account creation) as the first step
  • treatment_frozen and treatment_cumulative see the goals screen as the first step

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-131579

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-131579&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-131579&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/new-experiment-slug on your sandbox.

[matticbot]

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

App Entrypoints (~22 bytes added 📈 [gzipped])

name           parsed_size           gzip_size
entry-stepper        +47 B  (+0.0%)      +22 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

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.

[vykes-mac]

As described:

✅ Control group see account creation
✅ Treatment cumulative and Treatment frozen both the goals screen

[necronet]

LGTM