Unify label validation strategy across API functions

The `pgo create cluster` command was not using the same label validation as the other label commands were using. Issue: [ch10201]

Author: Jonathan S. Katz

internal/apiserver/clusterservice/clusterimpl.go

@@ -576,18 +576,12 @@ func CreateCluster(request *msgs.CreateClusterRequest, ns, pgouser string) msgs.
 return resp
 }
 
-userLabelsMap := make(map[string]string)
-if request.UserLabels != "" {
-labels := strings.Split(request.UserLabels, ",")
-for _, v := range labels {
-p := strings.Split(v, "=")
-if len(p) < 2 {
-resp.Status.Code = msgs.Error
-resp.Status.Msg = "invalid labels format"
-return resp
-}
-userLabelsMap[p[0]] = p[1]
-}
+userLabelsMap, err := apiserver.ValidateLabel(request.UserLabels)
+
+if err != nil {
+resp.Status.Code = msgs.Error
+resp.Status.Msg = err.Error()
+return resp
 }
 
 // validate any parameters provided to bootstrap the cluster from an existing data source