[API] Store Tag Serializer Code as a **tagging** app for Use Across Endpoints

[BethanyG]

Currently, we are assuming most endpoints will have Tags and we are also using taggit for tag management.

Our current taggit model required custom serializer code to make tags for resources display appropriately, and the expectation is that this same code (or some improved or different version) will be required for any endpoint that is using taggit or tags.

We should therefore move the TagSerializer and TagsSerializerField code out of resources, and into a common utility file or location for ease of import and use to other endpoints (and to better discuss and maintain it as a module).

Propose it be moved to the utils.py file, where we also have the jwt response handler code...or another common or core place.

Propose a tagging app for storing tagging related serializers, views, and functions.

[billglover]

Based on conversation on Slack it looks like a decision was made to move this to its own app (also known as a module).

[BethanyG]

Yes. Following the recommendation of Kenneth. Changed the issue title/description accordingly. This will be part of the PR that includes #71, #72 & #74.