Enable CLA for this project

[brylie]

In order to hold the Copyright to all contributions to this codebase, APInf needs developers to sign a Contributor License Agreement (CLA).

Goal

Require contributors to sign a CLA before accepting contributions to this project. The CLA process should be as simple as possible (read: low friction).

Resources

CLAHub offers an automated CLA checking service for Github projects.

[tulir]

We should probably wait for apinf/platform#2690 and see if we can use a similar CLA.

[brylie]

Ping @bajiat