test playbooks - `cocmd test`

**Background**
When writing a playbook, in the end of the day it's only yaml. and it's delivered to the community
as a software package. making sure it's 100% accurate and working is going to make the difference
for users who run playbooks and have their goal reached.

when @HillaShx tried my "contrib-onboarding" playbook for project new comers she got several problems
in the playbook content because it was written on my laptop and our settings are different.
This should not have happened.
And in the future it can only be achievable with tests for playbooks.

**Description**
add `cocmd test `
it should run the playbook on a docker based on the operating system specified in the playbook.
If no env is speicified- need to be tested for all operating systems:
- linux - https://hub.docker.com/_/ubuntu
- osx - https://hub.docker.com/r/sickcodes/docker-osx
- windows - https://hub.docker.com/_/microsoft-windows

**tests**
test the command with package from hub

**Docs**
add documentation for testing capabilities