README: break up WriteAuthorizationModelRequest into smaller understandable pieces

[adriantam]

Currently, the WriteAuthorizationModelRequest object used for (write authorization model)[https://github.com/openfga/python-sdk/blob/main/README.md#write-authorization-model] is large and difficult to understand. Ideally, we want to break it apart into smaller pieces

For example,

body = WriteAuthorizationModelRequest(
    schema_version = "1.1",
    type_definitions=[
        TypeDefinition(
            type="user",
        ),
        TypeDefinition(
            type="document",
            relations=dict(
                writer=Userset(
                    this=dict(),
                ),
                viewer=Userset(
                    union=Usersets(
                        child=[
                            Userset(this=dict()),
                            Userset(computed_userset=ObjectRelation(
                                object="",
                                relation="writer",
                            )),
                        ],
                    ),
                ),
            )
        ),
    ],
)

can be broken up as

user_type =  TypeDefinition(
    type="user",
)
document_type = TypeDefinition(
    type="document",
    relations=dict(
        writer=Userset(
            this=dict(),
        ),
        viewer=Userset(
            union=Usersets(
                child=[
                    Userset(this=dict()),
                    Userset(computed_userset=ObjectRelation(
                        object="",
                        relation="writer",
                     )),
                 ],
            )
        ),
    ),
)
        
body = WriteAuthorizationModelRequest(
    schema_version = "1.1",
    type_definitions=[
        user_type,
        document_type,
    ],
)

(and we break the document type relations into smaller pieces etc.)

The code in question is in

python-sdk/README.md

Line 299 in 1f4c734

body = WriteAuthorizationModelRequest(

Ideally, we will also fix the SDK generator so that newly generated python SDKs will have the corresponding changes. This is tracked as openfga/sdk-generator#126. However, if that is difficult to do, simply focusing on the Python SDK side https://github.com/openfga/python-sdk/blob/main/README.md will help us as well.

[JRudransh]

Please assign to me