Add flag com.android.healthfitness.flags.immediate_export to trunk_staging.

This change was automatically created by advancing the Gantry workflow at:
https://releasetracker.partner.android.com/changes/7id3tdi000001?build_unique_id=android_platform_health_fitness_aconfig
Do not edit this file manually or revert this change - use the Gantry workflow to manage the state of this flag.

Bug: 318484000
Flag: com.android.healthfitness.flags.immediate_export
Ignore-AOSP-First: AConfig change for future AOSP release
Change-Id: I28c34125bebfbf4ca9ee853b854a40f8aaafed87