Add support for API definition (like Open API 3.0) when accessing OGC API Features clients

[navispatial]

OGC API Features - Part 1 : Core describes support for API definitions.

The spec does not require Open API 3.x specification, but it's highly recommended to be provided by services.

So the client for OGC API Features should also support reading capabilities from Open API 3.x spec.

OGC API Features defines requirements (conformance) classes:
http://www.opengis.net/spec/ogcapi-features-1/1.0/req/oas30 => Servers conforming to this requirements class define their API by an OpenAPI Document

[navispatial]

Tools in Dart to handle Open API documents:

OpenAPITools:

• openapi-generator for dart

Devappliance.com

• openapi_generator package in pub.dev
• GitHub: openapi-generator-dart

Conduit

• larger framework: conduit
  • modern HTTP server application framework, ORM and OAuth2 provider with OpenAPI 3.0 integration. Foundation for REST, RPC or GraphQL services.
• as a part of the framework: conduit_open_api
  • Data structures for OpenAPI (Swagger) specification. Reads and writes JSON specifications.

[navispatial]

API definition is now accessible (as a parsed JSON Object tree).

Implemented in pre-release 0.12.0-dev.0 of geodata 0.12.0