Ariadne-codegen

- Added support for `Upload` scalar. Added support for file uploads to `AsyncBaseClient` and `BaseClient`.
- Added validation of defined operations against the schema.
- Removed `mixin` directive from fragment string included in operation string sent to server.
- Added support for `mixin` directive on fragments definitions.
- Added support for fragments defined on subtype of field's type.
- Added default representation for a field name consisting only of underscores.
- Changed generated client and models to use pydantic v2.
- Changed custom scalars implementation to utilize pydantic's `BeforeValidator` and `PlainSerializer`. Added `scalars_module_name` option. Replaced `generate_scalars_parse_dict` and `generate_scalars_serialize_dict` with `generate_scalar_annotation` and `generate_scalar_imports` plugin hooks.
- Unified annotations in generated client to be compatible with python < 3.9.
- Fixed generating default values of input types from remote schemas.
- Changed generating of input and result field names to add `_` to names reserved by pydantic.

- Fixed `AsyncBaseClient` and `BaseClient` to send `Content-Type` header with requests.

- Added support for subscriptions as async generators.
- Changed how fragments are handled to generate separate module with fragments as mixins.
- Fixed `ResultTypesGenerator` to trigger `generate_result_class` for each result model.
- Changed processing of models fields to trim leading underscores.
- Added `ShorterResultsPlugin` to standard plugins.
- Fixed handling of inline fragments inside other fragments.
- Changed generated unions to use pydantic's discriminated unions feature.
- Replaced HTTPX's `json=` serializer for query payloads with pydantic's `pydantic_encoder`.
- Removed `mixin` directive from operation string sent to server.
- Fixed `ShorterResultsPlugin` that generated faulty code for discriminated unions.
- Changed generator to ignore unused fragments which should be unpacked in queries.
- Changed type hints for parse and serialize methods of scalars to `typing.Any`.
- Added `process_schema` plugin hook.

- Changed logic how custom scalar imports are generated. Deprecated `import_` key.
- Added escaping of GraphQL names which are Python keywords by appending `_` to them.
- Fixed parsing of list variables.
- Changed base clients to remove unset arguments and input fields from variables payload.
- Added `process_name` plugin hook.

- Added generation of GraphQL schema's Python representation.
- Fixed annotations for lists.
- Fixed support of custom operation types names.
- Unlocked versions of black, isort, autoflake and dev dependencies
- Added `remote_schema_verify_ssl` option.
- Changed how default values for inputs are generated to handle potential cycles.
- Fixed `BaseModel` incorrectly calling `parse` and `serialize` methods on entire list instead of its items for `List[Scalar]`.

- Fixed generating models from interfaces with inline fragments.
- Added default `None` values for generated methods optional arguments.
- Added basic plugin system.
- Added `InitFileGenerator`, `EnumsGenerator`, `ClientGenerator` and `ArgumentsGenerator` plugin hooks.
- Added `InputTypesGenerator` and `ResultTypesGenerator` plugin hooks.
- Added `ScalarsDefinitionsGenerator` and `PackageGenerator` plugin hooks.
- Added support for `[tool.ariadne-codegen]` section key. Deprecated `[ariadne-codegen]`.
- Added support for environment variables to remote schema headers values.
- Added `--config` argument to `ariadne-codegen` script, to support reading configuration from custom path.