Update k8s deployment documentation

[jlstevens]

The documentation here suggests you always need the k8s_token secret to be defined.

I believe that this isn't always necessary and that the token will be automatically picked up from /var/run/secrets/kubernetes.io/serviceaccount/token when deployed from the anaconda-enterprise user (as the instructions recommend).

In addition, this means you don't necessarily need to go through the steps to get the token from kubectl. I'm not sure whether /var/run/secrets/kubernetes.io/serviceaccount/token existed in older versions of AE5 so it is possible these instructions are still required in some cases.