Revert "Revert "Add compatibility metadata to OTA package""

This reverts commit b1e59b8a.

This CL enables generating compatibility zip entry in an A/B OTA
package. We're not enabling the support for non-A/B OTAs for now until
they have the necessary support (e.g. /proc/config.gz exists).

Bug: 36810913
Test: Generate full and incremental packages for marlin and applly under
      normal boot and sideload respectively.

Change-Id: I69f0a3feb7a0efc7f727f92f31c9e63f47ee6530