Improve swagger doc usability

[dblodgett-usgs]

As reported by a client developer:

On the page https://labs.waterdata.usgs.gov/api/nldi/swagger-ui/index.html, I can't really find any info that I understand. For example, clicking on the first entry "lookup_controller," it says, "Returns characteristics types." That doesn't give me any insight into what it does or how it is useful.

[EthanGrahn]

There are annotations like this that Swagger provides to generate the docs. I can start creating better documentation to indicate this for future developers. We should also create a list of better descriptions for our current endpoints.