Add a global Code of Conduct file

[reshamas]

This file will be the default used in all the repositories in this organization.

If the repo project would like a different CoC (Code of Conduct), they can add it to their repo and it will override this one.

These repo's currently do have a CoC:

• https://github.com/WHO-Collaboratory/collaboratory-epiparameter-community
• https://github.com/WHO-Collaboratory/collaboratory-epipipeline-community

These repo's do not have a CoC:

• https://github.com/WHO-Collaboratory/collaboratory-mpox-genomics-community No CoC
• https://github.com/WHO-Collaboratory/simex
• https://github.com/WHO-Collaboratory/collaboratory-data-preparedness-community
• https://github.com/WHO-Collaboratory/collaboratory-mpox-genomics-phylomasking