dogfood-k8s: finalize migration over to new cluster

Created by: bobheadxi

Move all configuration, licenses, etc from the current k8s.sgdev.org to the new cluster we've set up at https://github.com/sourcegraph/deploy-sourcegraph-dogfood-k8s-2 in sourcegraph-dogfood's dogfood cluster.

• Move configuration, license => https://github.com/sourcegraph/sourcegraph/issues/13792#issuecomment-693140150
• Move DNS => https://github.com/sourcegraph/infrastructure/pull/2131
• Update handbook entry => https://github.com/sourcegraph/about/pull/1579
• Tear down old cluster