Move NDK ABI monitoring enabling flag to release flags

Currently NDK ABI monitoring is enabled by switching boolean flag in
soong code. When this flag is switched, it will enable ABI monitoring in
all release configurations at once.

This change moves the flag from soong code to the trunk-stable flags
framework ("build/release/build_flags.scl") that allows to enable it
only in specific configurations like "trunk-staging".

Test: TH
Bug: 156513478
Change-Id: Ibb810a834c0d756b22782b1a2d8ec5a5e575a4b3