16k: Sign the APKs to support 4k/16k page sizes

The page agnostic targets have to support 4k/16k page sizes. For
these targets, the APKs have to be aligned at 16k boundaries.

Bug: 302343940
Test: source build/envsetup.sh
      lunch aosp_cf_arm64_phone_pgagnostic
      m
      launch_cvd -userdata_format=ext4
Change-Id: Ia0e39a90c0d6a3e62d450157fdfd5e3ee36d346e