Updates the Permutive RTD module to facilitate for segmentation by
the new IAB Audience taxonomy.

To achieve this, this change introduces the concept of "transformations"
on the ORT2B `user.data` object. There are two components to these
transformations: a new `transformations` property on the Prebid config,
to be set by the publisher, and logic in the module for the actual
behaviour of the transformation.

We plan to use the transformation logic in this PR, combined with
configuration we'll share with publishers, to send IAB Audience
taxonomy cohort IDs to bidders.