releasetools: Add NonAbOtaPropertyFiles for non-A/B OTA packages.

This CL exposes ota-property-files flag for non-A/B OTA packages.
Currently the line only contains the info for the METADATA entry, for
example "ota-property-files=metadata:69:286". This allows system updater
to just download the METADATA entry, as opposed to downloading the
entire package, to learn about the info regarding the OTA package (e.g.
post-OTA build fingerprint). Note that this requires the OTA server-side
support to pass down the flag along with the update URL.

Bug: 74210298
Test: python -m unittest test_ota_from_target_files
Test: Generate a non-A/B package and check the property-files string.
Change-Id: I1482c587e18ea7101c8328777ea988c2d8ca06ac