codeintel: Explicitly list CNCF repositories for auto-indexing

Created by: efritz

This adds a hardcoded list of CNCF repos that we'd like to automatically index. Some of these will likely fail, at which point we need to evaluate the additional effort of maintaining an out-of-band manual process, or additional hard-coded conditions for particular repositories.

The effort of RFC 201 will subsume this effort (we will be able to configure the index process in the UI). I will follow up with a permanent solution, tracked in https://github.com/sourcegraph/sourcegraph/issues/14343.