Adding an additional CLI argument, ret_config, which can be used to
override configuration options passed to the returner.

Adding support for ret_config to all returners.

Adding _get_options to all returners that use configurable options.

Adding return_config support to the scheduler and scheduler related management module & state.
fixing lint issues.
more lint fixes.
Checkout that kwargs exists in clear_load before attempting to pull out a kwarg.
Merge pull request #15373 from garethgreenaway/returner_experiments

Ability to override default returner configuration options.