New idoverridegroup management module.

[t-woerner]

There is a new idoverridegroup management module placed in the plugins folder:

plugins/modules/ipaidoverridegroup.py

The idoverridegroup module allows to ensure presence and absence of idoverrides for groups.

Here is the documentation for the module:

README-idoverridegroup.md

New example playbooks have been added:

playbooks/idoverridegroup/idoverridegroup-absent.yml
playbooks/idoverridegroup/idoverridegroup-present.yml

New tests for the module can be found at:

tests/idoverridegroup/test_idoverridegroup.yml
tests/idoverridegroup/test_idoverridegroup_client_context.yml

[rjeffman]

@t-woerner please rebase this PR, as idoverrideuser caused the (expected) conflict.