Merge "Support key without default value for carrier config subset retrieval APIs" am: f303bd31e9 am: c7309dbf33

Original change: https://android-review.googlesource.com/c/platform/packages/services/Telephony/+/2479118

Change-Id: Ideb275d6284e4a5584d62be1c40e53a31414110d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>