Add pod_environment_secret secrets to be injected to all clusters.

A potential mechanism to provide secrets to custom sidecars. Right now
it is WIP and only provid secrets to Spilo Pods.

pkg/util/config/config.go

@@ -33,6 +33,7 @@ type Resources struct {
 	DefaultCPULimit         string            `name:"default_cpu_limit" default:"3"`
 	DefaultMemoryLimit      string            `name:"default_memory_limit" default:"1Gi"`
 	PodEnvironmentConfigMap string            `name:"pod_environment_configmap" default:""`
+	PodEnvironmentSecret    string            `name:"pod_environment_secret" default:""`
 	NodeReadinessLabel      map[string]string `name:"node_readiness_label" default:""`
 	MaxInstances            int32             `name:"max_instances" default:"-1"`
 	MinInstances            int32             `name:"min_instances" default:"-1"`

pkg/util/k8sutil/k8sutil.go

@@ -3,6 +3,7 @@ package k8sutil
 import (
 	"fmt"
 	"reflect"
+	"regexp"
 
 	apiextclient "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset"
 	apiextbeta1 "k8s.io/apiextensions-apiserver/pkg/client/clientset/clientset/typed/apiextensions/v1beta1"
@@ -22,6 +23,14 @@ import (
 	"github.com/zalando-incubator/postgres-operator/pkg/util/constants"
 )
 
+const (
+	EnvironmentNameRegexpString = "[-._a-zA-Z][-._a-zA-Z0-9]*"
+)
+
+var (
+	environmentNameRegexp = regexp.MustCompile(EnvironmentNameRegexpString)
+)
+
 // KubernetesClient describes getters for Kubernetes objects
 type KubernetesClient struct {
 	v1core.SecretsGetter
@@ -153,3 +162,7 @@ func SamePDB(cur, new *policybeta1.PodDisruptionBudget) (match bool, reason stri
 
 	return
 }
+
+func EnvironmentVariableNameIsValid(name string) bool {
+	return environmentNameRegexp.MatchString(name)
+}