My Site Dashboard: Tabs - Track experiment property with all events

[zwarm]

Parent #16007

This PR adds support for tracking My Site Default Tab Experiment properties with every event tracked (when the experiment is running)
The following property is tacked on to every event
default_tab_experiment values =dashboard|site_menu|nonexistent

I tried to keep this as generic as possible and not pollute the "tracker" with references to "MySIteDashboard".

Merge Instructions

• Ensure that PR My Site Dashboard: Tabs Add feature flags for default tab experiment #16175 and My Site Dashboard: Tabs - Assign default tab variant and save to app prefs #16176 have been merged
• - Remove the Not Ready for Merge label
• Merge as normal

To test:

• Launch the app and Login
• If not enabled, please enable MySiteDashboardTabsFeatureConfig, then restart the app and logout
• Login
• Navigate to My Site
• View the logs and note that you see property "default_tab_experiment" being tracked on all events
• Navigate to Me -> App Settings -> Debug Settings
• Disable my_site_default_tab_experiment and restart the app
• View the logs and note that you don't see property "default_tab_experiment" being tracked

Regression Notes

1. Potential unintended areas of impact
   Events are not tracked

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Manual and unit testing

3. What automated tests I added (or what prevented me from doing so)
   Add unit tests to MySiteDefaultTabExperimentTest

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-16183-build-120164.apk

• WordPress-pr-16183-build-120164.apk

[ashiagr]

👋 @zwarm

I found property default_tab_experiment getting tracked for all events when MySiteDashboardTabsFeatureConfig was enabled as described. 👍

It was only these login events which did not have the right variant, but it is something you already know and discussed in our call today:

🔵 Tracked: signed_in, Properties: {"dotcom_user":true,"default_tab_experiment":"nonexistent"}
🔵 Tracked: login_social_success, Properties: {"default_tab_experiment":"nonexistent"}

I'll approve and merge this PR and let you work on the remaining metrics stuff.