Implement q priority of request headers

[webb-ben]

Overview

Create common util functions get_choice_from_headers and get_from_headers to get value from header in case insensitive way and implement q priority sorting for header values. This logic is then applied to all headers that pygeoapi accepts q value ranking for: Accept and Accept-Language.

Related Issue / discussion

Closes #1948
Closes #1591

Additional information

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