[core]: ensure it's possible to extend an existing rule set with a global transform

[Ivan Plantevin]

Problem description
At the moment, global tag transforms result in a new (blueprint) data policy. We should make it possible to extend existing rule sets. That way, one can specify both tags and additional filters/transforms in for example DBT model metadata.

Proposed solution
Add a function that takes a rule set or data policy and adds the tag-based transforms to the existing rule set(s). Some validation/merge logic may be needed.