A constructor with the {@link MessageHeaders} instance to use.
<p><strong>Note:</strong> the given {@code MessageHeaders} instance is used
directly in the new message, i.e. it is not copied.
@param payload the message payload (never {@code null})
@param headers message headers
A constructor with the {@link MessageHeaders} instance to use. <p><strong>Note:</strong> the given {@code MessageHeaders} instance is used directly in the new message, i.e. it is not copied. @param payload the message payload (never {@code null}) @param headers message headers