Signal ASL in APK with manifest property

When bundling ASL in the APK by including a app.metadata file in assets,
the manifest must include an application property tag defining the path
of the file in the APK:

    <property android:name="android.content.SAFETY_LABEL_PATH"
    		android:value="some/path/filename" />

If this file is not found then the app metadata source will be set to
APP_METADATA_SOURCE_UNKNOWN and no ASL will be available for the app.

Bug: 329022140
Test: atest InstallAppMetadataTest
Test: atest AndroidPackageTest
Change-Id: I7646ea3fcc92d30f5b4f6f072e558e04a097978f