Follow-up from !22: missing default value for cielito_host_users_data

The following discussion from !22 (merged) should be addressed:

• @apias make this comment on a discussion:

  Right now, if cielito_host_username_list is defined in the inventory but not cielito_host_users_data, we will get a clear error:

  TASK [cielito.system.users_and_groups : Loop to build the primary groups of users of the host] ***********************************************
  task path: /home/apias/desarrolloudelar/ansible3/UdelaRInterior/ansible_collections/cielito/system/roles/users_and_groups/tasks/main.yml:19
  fatal: [salado.interior.edu.uy]: FAILED! => {"msg": "Error in jmespath.search in json_query filter plugin:\n{{ cielito_users_data | combine ( cielito_host_users_data, recursive=true )\n| dict2items ( key_name='username' )\n| community.general.json_query( cielito_users_query )\n| items2dict ( key_name='username' )\n}}\n: 'cielito_host_users_data' is undefined. 'cielito_host_users_data' is undefined"}

  So, for backward compatibility to really work, we just need to define a value for cielito_host_users_data in the defaults.

  I will open a new issue for this.