Enable yaml-lint Github action on push/pull-requests.

By running yamllint we add one more verification of quality to the
playbooks used on/provided by ansible-freeipa, that will be executed
on every push (even on forks) or pull-requests.

This patch provides the configuration needed to run yamllint on
the playbooks found in the `tests`, `playbooks` and `molecule`
directories, on every push or pull-request done on Github, using
ibiqlik/action-yamllint action version `v1`.

The current configuration for yamllint has many rules disable, so
the problems found can be fixed later. All rules after the comment
`# Disabled rules` should be enabled in the near future.