rootdir: Add ability to add additional adb_debug.prop values

For desktop devices we need to add some additional properties to the
adb_debug.prop file so we can enable ADB over TCP. This change makes it
so we can define additional properties using `soong_config_set`.

e.g.,
$(call soong_config_append,adb,additional_debug_properties,service.adb.listen_addrs=)
$(call soong_config_append,adb,additional_debug_properties,service.adb.tcp.port=5555)

Bug: 421998282
Test: m out/target/product/brya/vendor_boot-debug.img && verify adb_debug.prop contains new properties
Change-Id: I23168c36284d3e316c1338206c21e823040f9dea