Add demo mTLS client certificates and key

Included at the repository owner's request for demonstration and
integration testing only. Revocable on the robot side; not for
production use.

certs/client.key

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQCWMPaz89s03Ry9
+reK2kuTbq8DswFxl5OkuDKPZm4Bn62HxmD6AuQO8FeIOMW3mtlw7PZwLoPXihzrn
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+bUtQJBLiwzUdSvL6Awb3Z42kRL+rwTbVm/KekZUHw7V+x1ZyliOWU6nRyz8/ZizA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+-----END PRIVATE KEY-----