Implement native JSON schema support

[MaggieKimani1]

Tasks

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1. Add a JSON schema model class with all known keywords #1733
   V2-Enhancement +1
   
2. Parsing handlers for common properties #1763
   +0
   
3. Replace JsonSchema with OpenApiSchema #1793
   V2-Enhancement +1
   
4. Writer in Model class #1765
   +0
5. Local document dereference using JSON Pointer to component #1789
   V2-Enhancement type:feature +2
6. Local document dereference using $ref to $id #1790
   V2-Enhancement +1
   
7. External document dereference to OpenApiDocument using JSON Pointer #1791
   V2-Enhancement +1
   
8. Add host document to any model that can contain a reference.
9. Add a JsonSchemaReference proxy object for lazy reference resolution
10. Parsing handlers for unknown properties and extensions #1764
    +0
    
11. External document dereference to OpenApiDocument using $ref to $id #1812
    +0
    

[darrelmiller]

type property can be string or array in JSON Schema for 3.1

[captainsafia]

If it helps as a point of inspiration, here is the (internal) implementation of JsonSchema that might be a helpful basis for inspiration: https://github.com/dotnet/runtime/blob/c70791346cb716c02065c23d761d0743e30602ed/src/libraries/System.Text.Json/src/System/Text/Json/Schema/JsonSchema.cs