ipabackup_get_backup_dir: 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

- `suboptions` needs to be removed without arguments
- `author` needs to be given with the github user also: `Name (@user)`

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