add support for item schema string format (#1691)

[tomkralidis]

Overview

• add support for item schema string format
• add "Display Schema" block to collection HTML page

  Related Issue / discussion

  Fixes #1691

Additional information

cc @KoalaGeo

Dependency policy (RFC2)

• [x] 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
  • [ ] 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
• [x] I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[pvgenuchten]

assuming this relates to https://github.com/opengeospatial/ogcapi-features/blob/f810f6652c637cbc045e5baae726e83b9ccaa6d0/extensions/transactions/create-replace-update-delete/standard/requirements/features/REQ_schema.adoc?

[tomkralidis]

assuming this relates to https://github.com/opengeospatial/ogcapi-features/blob/f810f6652c637cbc045e5baae726e83b9ccaa6d0/extensions/transactions/create-replace-update-delete/standard/requirements/features/REQ_schema.adoc?

@pvgenuchten yes. Note that we initially implemented the .../schema endpoint in February for items and coverages as part of 0.16.0.

[KoalaGeo]

See https://github.com/geopython/pygeoapi/issues/1691#issuecomment-2188596324