Add config schema for parent_role_mapping / child_role_mapping options

Problem/Motivation

ggroup_role_mapper adds parent_role_mapping / child_role_mapping configuration options, but does not define a config schema for this configuration

Proposed resolution

Add config schema for parent_role_mapping / child_role_mapping options

Remaining tasks

1. Write a patch
2. Review
3. Commit

User interface changes

None.

API changes

None.

Data model changes

None.