Synchronize XSD and DMR description of obtain-kerberos-ticket attribute

                        "obtain-kerberos-ticket" => {
                            "type" => BOOLEAN,
                            "description" => "Should the KerberosTicket also be obtained and associated with the credential.",
                            "expressions-allowed" => true,
                            "required" => false,
                            "nillable" => true,
                            "default" => false,
                            "access-type" => "read-write",
                            "storage" => "configuration",
                            "restart-required" => "resource-services"
                        },

                <xs:attribute name="obtain-kerberos-ticket" type="xs:boolean" default="false">
                    <xs:annotation>
                        <xs:documentation>
                            Should the KerberosTicket also be obtained and associated with the credential.

                            This is required to be true where credentials are delegated to the server.
                        </xs:documentation>
                    </xs:annotation>
                </xs:attribute>