Update the License to explicitly accept contributions

[brucellino]

Issue type

How would you best describe your issue ?

• [ ] Problem with one of the services
• [ ] Ansible problem
• [ ] Puppet problem
• [ ] Container problem
• [ ] Want to join as collaborator
• [x] General question, enhancement or suggestion

The current license is MIT. I propose that we move to Apache-2 and update the Contributors.md to explicitly take into account issues regarding contributing code.