Updates the migration status to started on the DIY flow

[valterlorran]

Related to #95156

Proposed Changes

• Updates the migration status sticker to started on the Instructions step for the self-serve flow.

Why are these changes being made?

• As part of the Post-purchase project, we need to store the state of the migration using the stickers to allow us to better redirect the user back to the flow.
• For the Post-migration experience, we need to know the status of the migration so we can show the Launchpad with for the migrated sites.

Testing Instructions

• Apply this diff to your local environment or use Calypso live
• Start a migration and go through the "Do it myself" flow
• Once you reach the "Instructions" step, go to the blog's RC and verify that you have the following events in the Audit Trail panel:
  • add sticker - migration-pending-diy
  • remove sticker - migration-pending-diy
  • add sticker - migration-started-diy

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-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-121441

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-121441&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-121441&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
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug add/sticker-migration-start-diy on your sandbox.

[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.

[m1r0]

Works as described. 👍