Add the CLA files to the repo and add a legal-check job to the CI
The CLA is a legal document required to ensure the project holds the correct right on the code to release it under the Apache license. This MR aims at checking that the contributors have signed the CLA.
- Make available the CLA documents in the repo (under Documentation/CLA).
- Update the CONTRIBUTING.MD to explain the importance of the CLA.
- Set up a
legal-check
CI job to ensure all the contributors have signed the CLA (fix #291 (closed)).