ipaclient_test: Fix documentation sections and agument spec

ansible-test with ansible-2.14 is adding a lot of new tests to ensure
that the documentation section and the agument spec is complete. Needed
changes:

DOCUMENTATION section

- `type: str` needs to be set for string parameters
- `type: list` needs to be set for list parameters
- `elements: str` needs to be given for list of string parameters
- `required` tags need to be fixed according to the `argument_spec`
- `type` tag needs to match `argument_spec`
- `default` tag needs to match `argument_spec`
- `author` needs to be given with the github user also: `Name (@user)`

RETURN section

- `elements: str` needs to be given for list of string parameters
- `type: string` is not valid and needs to be replaced by `type: str`
- `returned` needs to be set

argument_spec

- `type='str'` needs to be set for string parameters
- `elements='str'` needs to be added to all list of string parameters

supports_check_mode is turned off as it is not supported.

A call to ansible_ipa_client.check_imports has been added to check for import
errors.

The `copyright` date is extended with `-2022`.