add elevation profiles to park unit connections

[RobLBaker]

currently set_content_units gets the geographic bounding boxes of park units, but it does not get the elevational bounding boxes (lowest and highest points) of a park unit. It would be nice to include this information.

hit USGS api: https://epqs.nationalmap.gov/v1/docs

https://lpdaac.usgs.gov/resources/e-learning/getting-started-with-the-a%CF%81%CF%81eears-api-submitting-and-downloading-an-area-request/

[RobLBaker]

Although solvable using Amazon Web Services, trusted sources such as USGS currently do not have easy access to generating elevation minimum and maximums for polygons. Additionally, park polygons accessible via the NPS API aren't nearly as accurate as one might hope for.