Support Admin-only Swagger Docs

We have some API endpoints that are only for Admin users. It would be nice to be able to hide the Swagger docs of those endpoints from non-Admin users. This came up along with some potential solutions in this discussion (https://github.com/Asymmetrik/node-rest-starter/pull/114#discussion_r598895869).

**Acceptance Criteria**
- Determine if filtering by tags, extending/customizing the Swagger UI, or some other option is a viable solution
- If so, make necessary updates enable hiding admin-only endpoints from non-admin users
- If not feasible/reasonable/possible, mention why and close issue.

Start by reading the linked pull-request discussion about filtering by tags and customizing Swagger UI, then inspect the repository's Swagger integration. Determine whether admin-only endpoints can be hidden from non-Admin users without weakening access controls. Done means implementing a viable approach or documenting why it is not feasible and closing the issue.

Written by the indexing model from the issue text.