Verbatim JSON-LD injection feature

[avillar]

Overview

This PR enables injecting JSON-LD context into both JSON and JSON-LD Features and STAC items, without applying any modifications to the JSON-LD version. This behavior is disabled by default, and has to be specifically enabled in the linked-data configuration section.

Related Issue / discussion

Additional information

Dependency policy (RFC2)

• [ ] I have ensured that this PR meets RFC2 requirements

Updates to public demo

• [X] I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • [X] 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)

• [X] 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