Adding MessagingServiceSchema example

<?xml version="1.0" encoding="UTF-8"?>

<xs:schema xmlns="http://MessagingServiceSchema.example.com/schema/v1.1.1/" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://MessagingServiceSchema.example.com/schema/v1.1.1/" elementFormDefault="qualified">

    <xs:element name="messagingServiceDefinedParameters" type="MessagingServiceDefinedParameters"/>

    <xs:complexType name="MessagingServiceDefinedParameters">

        <xs:sequence>

            <xs:element name="messageID" type="xs:string"/>

            <xs:element name="messageContent" type="xs:string"/>

            <xs:element name="attachment" type="MessageAttachment" minOccurs="0"></xs:element>

        </xs:sequence>

    </xs:complexType>

    <xs:complexType name="MessageAttachment">

        <xs:element name="attachmentType" type="xs:string" minOccurs="0" />

        <xs:element name="attachmentData" type="xs:base64Binary" minOccurs="0" />

    </xs:complexType>

</xs:schema>