Create CODE_OF_CONDUCT.md

[tracykteal]

Adding the standard Contributor Covenant Code of Conduct with ops@nixtla.io as the contact.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}