Enable AndroidAppRatingPrompt in fieldtrial_testing_config.json

Change-Id: I5de668e0c9039c807431361ede1cf829ab4f102c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7719442
Reviewed-by: Jenna Himawan <jhimawan@google.com>
Auto-Submit: Gazal Agarwal <agazal@google.com>
Commit-Queue: Jenna Himawan <jhimawan@google.com>
Cr-Commit-Position: refs/heads/main@{#1608571}
NOKEYCHECK=True
GitOrigin-RevId: c9e34ffe540354f119b103885b7604b1261e8b67