Product license verification in Console (#518)

Operator UI - Provide and store License key
- New License section in Operator UI will allow user to provide the
  license key via input form
- New License section in Operator UI will allow the user to fetch the
  license key using subnet credentials
-  Console backend has to verify provided license is valid -
   https://godoc.org/github.com/minio/minio/pkg/licverifier#example-package
-  Console backend has to store the license key in k8s secrets

Operator UI - Set license to tenant during provisioning
- Check if license key exists in k8s secret during tenant creation
- If License is present attach the license-key jwt to the new console
tenant via an environment variable

Operator UI - Set license for an existing tenant
- Tenant view will display information about the current status of the
  Tenant License
- If Tenant doesn't have a License then Operator-UI will allow to attach
new license by clicking the Add License button
- Console backend will extract the license from the k8s secret and save
the license-key jwt in the tenant console environment variable and
redeploy

restapi/consts.go

@@ -26,6 +26,7 @@ const (
 	ConsolePort           = "CONSOLE_PORT"
 	ConsoleTLSHostname    = "CONSOLE_TLS_HOSTNAME"
 	ConsoleTLSPort        = "CONSOLE_TLS_PORT"
+	ConsoleSubnetLicense  = "CONSOLE_SUBNET_LICENSE"
 
 	// Constants for Secure middleware
 	ConsoleSecureAllowedHosts                    = "CONSOLE_SECURE_ALLOWED_HOSTS"
@@ -59,3 +60,9 @@ const (
 	KESImageVersion     = "minio/kes:v0.12.1"
 	ConsoleImageVersion = "minio/console:v0.4.6"
 )
+
+// K8s
+
+const (
+	OperatorSubnetLicenseSecretName = "subnet-license"
+)