Refactor name of from/to_pb_message and from/to_pb_value to be descriptive one is used in the workflow definitions and the other in params_dict

[lfse-slafleur]

{from,to}_pb_message are used for workflow definitions while {from,to}_pb_value are used to pack a params_dict value into protobuf Struct to accompany a JobSubmission. These names are not descriptive at all and should be altered to showcase their intended goal.