Add Service Template TOSCA handling

Today we can only handle a single service template in the database. We
should be able to handle multiple service templates and assign arbitrary
policy types and policies to maned and versioned service templates.

This review brings in the Java API in models provider for handling
service templates in this way and uses a simplistic single-teplate
implementation in models-tosca, that will work but still only handles a
single service template under the hood.

Issue-ID: POLICY-2900
Change-Id: Ia02dea8abe44b7f407e685090a4b8e0360889653
Signed-off-by: liamfallon <liam.fallon@est.tech>