Consolidate config, openapi, and asyncapi logic

[webb-ben]

Overview

Organize the implementations of pygeoapi.config, pygeoapi.openapi, pygeoapi.asyncapi with each other. Each implements the methods (where X is the case sensitive name of the module):

• get_x: Read and serialize the document
• get_x_schema: Read and serialize the schema document
• validate_x_document: Validate document against schema

Furthermore some alignment was done on the CLI options for these functions.

• Each now falls back to the respective PYGEOAPI_X environment variable if an override is not provided during execution.
• Deprecate --output-file in favor of feature specific flag.
• Derive format from output file type. Only recognize --format when no file to write.

TODO: Add AsyncAPI tests

Related Issue / discussion

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