Implement multi-wsgi app setup to offer endpoint-per-dataset strategy

[reinvantveer]

Overview

Resolves #2148

Additional information

The implementation provides a wrapper function around statements in pygeoapi/flask_app.py to allow calling it as many times as necessary to create a per-dataset endpoint. For each call, it returns a Flask wsgi app that can be served as usual. Since Pythonic conventions use module-scoped variables in all-caps, these have now been snake-cased as they are wrapped by the make_wsgi_app function.

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