Add missing SA for dns internal check

[titilambert]

Hello,

I get this kind of error with the dns-status-internal check:

time=" " level=error msg="Error waiting for node to reach minimum age: nodes \"aks-linux1-18020575-vmss0003io\" is forbidden: User \"system:serviceaccount:synthetic:default\" cannot get resource \"nodes\" in API group \"\" at the cluster scope"

It seems the dns-status-internal check, does a 'get node' query:
See there:

• https://github.com/kuberhealthy/kuberhealthy/blob/master/cmd/dns-resolution-check/main.go#L111

• kuberhealthy/pkg/checks/external/nodeCheck/main.go

  Line 53 in 12c5a48

  node, err := client.CoreV1().Nodes().Get(ctx, nodeName, v1.GetOptions{})

The PR adds the missing Service Account and RBAC for this check

[integrii]

LGTM

[integrii]

Thank you!