Enable applying tags to profiles

It could be helpful for key users to be able to "tag" profiles with one or more tags - arbitrary strings - that could then be used for building audiences and populating queries.  This would enable those users to collect the audiences they need without having our IT group add more fields to the Profile resource.

For instance, we might need to send a communication to "power users" of several applications on a periodic basis about upgrades or downtimes.  There is no yes/no flag on our Profile resource corresponding to a power user.  The profiles of these power users could be tagged as "Power User" without the need to add a database field or create a brand-new audience.

This could operate similarly to how blog posts can be tagged with certain subjects then searched or filtered by those subjects... or how tags on these forum posts are used.