add sanitization to to_json output

[tomkralidis]

Overview

This PR adds sanitization to pygeoapi.util.to_json.

Related Issue / discussion

Additional information

None

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

[webb-ben]

From what I recall, tojson might not be able to serialize a date time (as implemented in

pygeoapi/pygeoapi/util.py

Line 363 in 27be632

def json_serial(obj: Any) -> str:

? Might be worth building some tests for HTML

[tomkralidis]

Then will shift to to_json. Update coming with tests.