Proposal for closing #3837

Makes the config values used by JobQueue publically accessible so that users can use them in addition to their custom values. Also adds warnigs that explain what this is about.

@rejedai, would you mind also having a look at this, given that you reported the issue?

• Added .. versionadded:: NEXT.VERSION, .. versionchanged:: NEXT.VERSION or .. deprecated:: NEXT.VERSION to the docstrings for user facing changes (for methods/class descriptions, arguments and attributes)
• Created new or adapted existing unit tests
• Documented code changes according to the CSI standard <https://standards.mousepawmedia.com/en/stable/csi.html>__
• Added myself alphabetically to AUTHORS.rst (optional)
• Added new classes & modules to the docs and all suitable __all__ s
• Checked the Stability Policy <https://docs.python-telegram-bot.org/stability_policy.html>_ in case of deprecations or changes to documented behavior

closes #3837