fix: allow object and array without type name

[hgiasac]

Many object and array types don't have the type field. The tool should detect if additionalProperties or items field is not empty instead.
The PR also refactors and gets rid of redundant codes in the OpenAPI schema builder

[github-actions]

Package	Line Rate	Health
github.com/hasura/ndc-http/connector	63%	➖
github.com/hasura/ndc-http/connector/internal/argument	53%	➖
github.com/hasura/ndc-http/connector/internal	57%	➖
github.com/hasura/ndc-http/connector/internal/compression	64%	➖
github.com/hasura/ndc-http/connector/internal/contenttype	56%	➖
github.com/hasura/ndc-http/connector/internal/security	60%	➖
github.com/hasura/ndc-http/ndc-http-schema/configuration	41%	➖
github.com/hasura/ndc-http/ndc-http-schema/openapi/internal	45%	➖
github.com/hasura/ndc-http/ndc-http-schema/openapi	40%	➖
github.com/hasura/ndc-http/ndc-http-schema/schema	32%	❌
github.com/hasura/ndc-http/ndc-http-schema/utils	44%	➖
Summary	48% (4447 / 9216)	➖

Minimum allowed line rate is 40%