Update schema to accept a list for 'listen'

[zigarn]

'listen' for handlers is actually a list:

• https://github.com/ansible/ansible/blob/aa268b8db27193dd3f842ad72860ec3aefc3620d/lib/ansible/playbook/handler.py#L29
• https://github.com/ansible/ansible/blob/aa268b8db27193dd3f842ad72860ec3aefc3620d/examples/play.yml#L513

Also update doc link.

[ssbarnea]

Thanks! Don't worry about CI. I will fix it.

[zigarn]

Proposed konstruktoid/ansible-role-hardening#223 to fix a bit of the eco job.