We are not asking you to give us your copyright, but we need to get your OK to distribute and potentially relicense your code without restriction. So please make sure you have signed our contributor agreement.
All contributors of CrateDB sign a Contributor License Agreement (CLA). That's how we assure the users of CrateDB about the origin and continuing existence of the code. You only need to sign the CLA once.
What type of contributor are you?
Company with employees contributing
Individual Corporate Contributor under an existing company contributor agreement (your employer)