Returns the tags currently set on a support request.

DoiT employee (doer) callers receive the full tag set verbatim,
including internal namespaces (e.g. tier/*, synapse_*). Customer
callers receive only tags under the customer_tag/ namespace, with
that prefix stripped (e.g. a tag added as billing reads back as
billing). Always present; empty array when the caller has no visible
tags.