[2/5] Implement catalog zones options new syntax based on custom properties

According to DNS catalog zones draft version 5 document, catalog zone custom properties must be placed under the "ext" label.

Make necessary changes to support the new custom properties syntax in catalog zones with version "2" of the schema.

Change the default catalog zones schema version from "1" to "2" in ARM to prepare for the new features and changes which come starting from this commit in order to support the latest DNS catalog zones draft document.

Make some restructuring in ARM and rename the term catalog zone "option" to "custom property" to better reflect the terms used in the draft.

Change the version of 'catalog1.zone.' catalog zone in the "catz" system test to "2", and leave the version of 'catalog2.zone.' catalog zone at version "1" to test both versions.

Add tests to check that the new syntax works only with the new schema version, and that the old syntax works only with the legacy schema version catalog zones.

Closes #3222 (closed)