[WIP] add support for STAC API v1.0.0

[tomkralidis]

Overview

This PR provides a minimal implementation of STAC API 1.0.0. The design pattern is to leverage resources already defined via feature or record providers, and updating the resource type to stac-collection, which will get picked up by the STAC search functions in pygeoapi.api.stac:search.

Related Issue / discussion

#221

Additional information

cc @dblodgett-usgs

Dependency policy (RFC2)

• I have ensured that this PR meets RFC2 requirements

Updates to public demo

• I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • https://github.com/geopython/demo.pygeoapi.io/blob/master/services/pygeoapi_master/local.config.yml

Contributions and licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines