func (p *Message) WithMetadata(metadata MapMatcher) *Message {
	p.Metadata = metadata
	return p
}
func (p *Message) WithMetadata(metadata MapMatcher) *Message {
	p.Metadata = metadata
	return p
}
func ( p * Message ) WithMetadata ( metadata MapMatcher ) * Message { p . Metadata = metadata return p }
// WithMetadata specifies message-implementation specific metadata
// to go with the content
WithMetadata specifies message - implementation specific metadata to go with the content