Create a way to initialize entities through Translate API

[ahives]

Currently, there is a use case to take values from one segment and use them to initialize another segment. This can be partially done already in terms of setting fields but the missing piece is building and initializing a new entity from scratch. A concrete example would be I want to take some field values from a MSH segment and use them to build a MSA segment to send a response to the sender. In order to do this I need to be able to initialize the MSA segment and then set the values I am interested in.