Introduce activity log filters feature flag

[malinajirka]

Related to #13268

This PR introduces a local feature flag for the Activity Log filters feature. When the feature flag is enabled a "Date range" chips is shown in the activity log.

Note: It doesn't matter if it gets merged into 16.1 or 16.2.

To test:

1. Open Activity Log and make sure the "Date range" chip is hidden
2. My Site -> Avatar icon in the toolbar -> App Settings -> Test feature configuration
3. Enable ActivityLogFiltersFeatureConfig and click on "Restart app"
4. Go back to Activity Log and notice "Date range" chip is shown

PR submission checklist:

• I have considered adding unit tests where possible.
• 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 APK here.

[ashiagr]

👍

Tested the changes, I was able to see "Date range" chip after enabling ActivityLogFiltersFeatureConfig.