Add aftl inclusion proof

The otatools should talk to the aftl server and append the inclusion
proofs when building the vbmeta image. We should only do this during the
signing process when the network is always available.

Also the inclusion proof doesn't impact the final vbmeta image size on
coral, where the final size is 8192 after padding. This is below the
physical image of 65536.

Bug: 147870995
Test: unit tests pass, run sign_target_file_apks
Change-Id: If84c6bf5198c9b05f5e0c16ae6335971915f47e3