Add Support for Manta Object Storage as a Gateway (#5025)

Manta is an Object Storage by [Joyent](https://www.joyent.com/)

This PR adds initial support for Manta. It is intended as non-production 
ready so that feedback can be obtained.

vendor/github.com/joyent/triton-go/triton.go

@@ -0,0 +1,18 @@
+package triton
+
+import (
+	"github.com/joyent/triton-go/authentication"
+)
+
+// Universal package used for defining configuration used across all client
+// constructors.
+
+// ClientConfig is a placeholder/input struct around the behavior of configuring
+// a client constructor through the implementation's runtime environment
+// (SDC/MANTA env vars).
+type ClientConfig struct {
+	TritonURL   string
+	MantaURL    string
+	AccountName string
+	Signers     []authentication.Signer
+}