[Gallery Refactor] Analytics

[antonis]

Depends on #15129

Description

This adds the results of the unstableGalleryWithImageBlocks setting to the editor_session_start event so that we can monitor how many of our users have migrated to the new gallery refactor over time.

Note: The changes match the analytics collected with wordpress-mobile/WordPress-iOS#16848

To test:

Setup

1. A site running Gutenberg generated from [Mobile] Android: Pass the Gallery v2 Flag over from the editor WordPress/gutenberg#33544
2. On your site enable the Gallery Refactor by going to Gutenberg > Experminents > Check "Test a new gallery block that uses nested image blocks"

Enable Gallery Refactor

1. Navigate to the Editor
2. Expect to see the event editor_session_start contain the property unstableGalleryWithImageBlocks with the value true

Disable Gallery Refactor

1. Navigate to the Editor
2. Expect to see the event editor_session_start contain the property unstableGalleryWithImageBlocks with the value false

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APKs:

• Jetpack-pr-15134-build-114819.apk
• WordPress-pr-15134-build-114819.apk

[antonis]

@mkevins I added a fix for the NullPointerException detected on a fresh install run with a61cdcd

Adding a screenshot of the crash for context

[mkevins]

Thanks for the fix Antonis! I tested it with the latest changes, and everything is working as expected. LGTM!