Ariadne-graphql-proxy

- Fixed handling of nested variables in objects and lists.
- Added `queries`, `mutations` and `subscriptions` APIs to `ProxySchema.add_remote_schema`, `ProxySchema.add_schema` and `copy_schema` for creating schemas that are subsets of other, larger schemas.

- Added `CacheSerializer`, `NoopCacheSerializer` and `JSONCacheSerializer`. Changed `CacheBackend`, `InMemoryCache`, `CloudflareCacheBackend` and `DynamoDBCacheBackend` to accept `serializer` initialization option.
- Fixed schema proxy returning an error when variable defined in an operation is missing from its variables.
- Fixed query `union` fields support.
- Improved custom headers handling in `ProxyResolver` and `ProxySchema`.
- Proxy errors and extensions from upstream.
- Added fields dependencies configuration option to `ProxySchema`.

- Added `CloudflareCacheBackend`.
- Added `DynamoDBCacheBackend`.
- Changed `QueryFilter` and `root_resolver` to split variables between schemas.
- Added `insert_field` utility to `ProxySchema`. Added `get_query_params_resolver` as factory for `imgix` resolvers.

- Initial release.