Missing schema for social_group.settings

Problem

There is no schema declaration for the social_group.comment_settings config object.

Proposed solution

Add a config/schema/social_group.schema.yml file with the following contents:

social_group.settings:
  type: config_object
  label: 'Social Group Settings'
  mapping:
    allow_group_selection_in_node:
      type: boolean
      label: 'Allow logged-in users to change or remove a group when editing content.'

Needed discussion

Discuss whether the labels/descriptions are correct.