Upgrade restrictedpython to 4.0b2

[fabaff]

Description:

• Upgrade restrictedpython to 4.0b2
• Update ordering
• Add link to documentation
• Small update of docstrings

Example entry for configuration.yaml (if applicable):

python_script:

Checklist:

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable ([example][ex-requir]).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.

[fabaff]

I'm not sure if _getattr_ requires special attention.