[nearby] Add discoveryTimestamp field am: a34d7e8949

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2871218

Change-Id: I9a3ace5c7fc126b1936991d12f9c9aa98f1022c0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>