Validate users dictionary JSON using jsonschema

See:

• https://www.ipspace.net/kb/DataModels/70-Validation.html
• https://json-schema.org/understanding-json-schema/index.html
• https://blog.ipspace.net/2021/03/ansible-validation.html
• https://github.com/ansible-collections/ansible.utils/blob/main/docs/ansible.utils.validate_module.rst