bump dashboard version and add automation to update it

[medyagh]

latest version shows kubernetes-dashboard-7.14.0
http://github.com/kubernetes/dashboard

our version seems to be 2

minikube/pkg/minikube/assets/addons.go

Line 168 in a9a9133

"Dashboard": "kubernetesui/dashboard:v2.7.0@sha256:2e500d29e9d5f4a086b908eb8dfe7ecac57d2ab09d65b24f588b1d449841ef93",

[afbjorklund]

You will need helm for this version (7+), no kubectl.