Add configuration to support running WAL-E.

- Set WAL_S3_BUCKET to point WAL-E where to fetch/store WAL files
- Set annotations/iam.amazonaws.com/role to set the role to access AWS"

The new env vairables are PGOP_WAL_S3_BUCKET and PGOP_KUBE_IAM_ROLE.

pkg/util/config/config.go

@@ -41,6 +41,8 @@ type Config struct {
 	ServiceAccountName string `split_words:"true" default:"operator"`
 	DbHostedZone       string `split_words:"true" default:"db.example.com"`
 	EtcdScope          string `split_words:"true" default:"service"`
+	WALES3Bucket       string `envconfig: "wale_s3_bucket"`
+	KubeIAMRole  	   string `envconfig: "kube_iam_role"`
 	DebugLogging       bool   `split_words:"true" default:"false"`
 }