Add Contributor License Agreement as a GitHub Action

[Picaut]

Is your feature request related to a problem? Please describe. Allows contributor to sign a CLA within a Pull Request

Describe the solution you'd like https://github.com/cla-assistant/github-action

Alternative solution: https://github.com/cla-assistant/cla-assistant

[Picaut]

@gpetit I don't remember if we have somewhere a CLA for NoiseModelling. If not, It should be done. May be use http://selector.harmonyagreements.org/ for creating one (as for I-Simpa). It could be store in a file somewhere in the NoiseModelling repository or website or wiki