MLECO-1766: Default build flow helper scripts added

MLECO-1882: Anomaly Detection use-case default model download added 
and tests updated to run with it.

Test data generation cmake logic moved from use-case cmakes to top-level cmake script.

Signed-off-by: Isabella Gottardi <isabella.gottardi@arm.com>
Change-Id: Ifde469e3585c37b9a53810236a92ce52d4fbb407