Add option to disable `__typename` in generated queries

[jacksonpradolima]

Description:
Currently, ariadne-codegen always includes the __typename field in generated queries and models. This is usually correct and aligns with the GraphQL specification, since __typename is a valid meta-field on all object types and helps with cache normalization and type resolution.

However, when integrating with some GraphQL APIs that are not fully spec-compliant, adding __typename can cause errors. For example, some servers throw exceptions or reject queries when __typename is included on nested objects.

In these cases, it would be very useful to have a configuration option to disable automatic insertion of __typename (e.g., include_typename: false in the config file).

Motivation:

• Improves compatibility with non-standard GraphQL implementations.
• Makes ariadne-codegen more flexible for real-world integration scenarios where the API cannot be changed.
• Still allows the default behavior (with __typename enabled) for users who work with spec-compliant APIs.

Proposed solution:

• Add a configuration flag (e.g., include_typename: true|false) to the codegen config.
• Default should remain true to preserve current behavior and spec alignment.
• If false, codegen should skip adding __typename fields in queries and models.

Example:

# codegen.yml
schema_path: schema.graphql
queries_path: queries.graphql
target_package_path: generated
include_typename: false   # <--- new option

This would allow users to generate queries without __typename when required by specific APIs.