Feature: add field or flag to easily add one more field in certSANs of api-server

[Kun483]

So far, according to the doc https://microk8s.io/docs/services-and-ports#heading--auth, we need to manually modify the file /var/snap/microk8s/current/certs/csr.conf.template and then run sudo microk8s refresh-certs --cert server.crt. When we want to have a reverse proxy sever so that every request, like kubectl command, to api server will be routed to the reverse proxy. In this case, is there a way we can have a field like snapstoreProxyDomain or a flag so that we can easily change the certSANs of api-server?