Apply OpenAPI spec (#3317)

Adds scripts that sync PyGithub classes with GitHub OpenAPI spec:
- `scripts/openypo.py`: main script to sync PyGithub class with OpenAPI
spec
- `scripts/openapi-update-classes.sh`: wrapping script to update
multiple / all classes
- `scripts/get-openapi-path.sh`: extract API path from OpenAPI spec
- `scripts/get-openapi-schema.sh`: extract API schema from OpenAPI spec
- `scripts/update-assertions.sh`: update assertions in test files
- `scripts/prepare-for-update-assertions.py`: pre-processor script to
allow running the update assertions script
- `scripts/sort_class.py`: apply method and attribute order to PyGithub
classes, simplifies managing classes by code