Add non-Gaussian covariance to TJPCov

[carlosggarcia]

Add non-Gaussian covariance to TJPCov

CCL now support computing the non-Gaussian covariance. We need to interface it to TJPCov

Contacts: @carlosggarcia
Day/Time: Thursday, Oct 31 at 9-12am UK time
Main communication channel: Slack
GitHub repo: LSSTDESC/TJPCov#106
Zoom room (if applicable):

Goals and deliverable

Implement the non-Gaussian covariance in TJPCov

Resources and skills needed

Python and CCL and a bit of halo model.

Detailed description

Apart from building the interface, we might need to do some approximations as we did with the SSC to avoid having to specify halo profiles, etc.