feat: custom Schema Parser support

[VisualBean]

About the PR

AsyncAPI 3.0 supports additional schemas, also outside of the traditional ones.
This feature refactors existing schema parsing and adds a new SchemaParserRegistry.

A new readersetting propery has been added SchemaParserRegistry here you can register additional parsers if you have a need for new schemas that either aren't supported or something completely custom.

var settings = new AsyncApiReaderSettings();
settings.SchemaParserRegistry.RegisterParser(new MySchemaParser());

note that jsonschema and avro still is the default support.

Changelog

• Add: new SchemaParserRegistry for holding schema parsers aside from the default JsonSchema and avro
• Refactor: existing parsers to use the new model.
• Refactor: MultiFormatSchema Deserializer now uses the SchemaParserRegistry.