Resource generation - default to yaml, add option for output formats (JSON or YAML)

[jasonmadigan]

• Resource generation output format options - default to yaml, add option for output formats (JSON or YAML)
• Associated docs

Verify

1. Build locally:

go build or one of the make targets

2. Sample generation commands:

./kuadrantctl generate gatewayapi httproute --oas examples/oas3/petstore.yaml # defaults to yaml
./kuadrantctl generate gatewayapi httproute --oas examples/oas3/petstore.yaml -o json
./kuadrantctl generate kuadrant ratelimitpolicy --oas examples/oas3/petstore.yaml
./kuadrantctl generate kuadrant authpolicy --oas examples/oas3/petstore-with-oidc-kuadrant-extensions.yaml
./kuadrantctl generate kuadrant ratelimitpolicy --oas examples/oas3/petstore-with-rate-limit-kuadrant-extensions.yaml

# via stdin
cat examples/oas3/petstore-with-rate-limit-kuadrant-extensions.yaml | ./kuadrantctl generate kuadrant ratelimitpolicy --oas -
cat examples/oas3/petstore-with-rate-limit-kuadrant-extensions.yaml | envsubst | ./kuadrantctl generate kuadrant ratelimitpolicy --oas -

[jasonmadigan]

@maleck13 fyi: some of this might be of interest for the demo too

[eguzki]

LGTM.

Left some minor comments to discuss before approving. But this is ready to be merged.

Verification steps worked as expected. Thanks for those.

[jasonmadigan]

@eguzki made a few tweaks - thanks for the earlier review