Add parsedData to Hl7v2Message to allows users not using schematized parsing to utilized HL7v2IO

Hl7v2Message class is used as model for data returned from healthcare API HL7v2 message methods. Currently it only supports the ability to utilize the schematizedData field from the response object. Adding support for the parsedData field will open use of the HL7v2IO Connector to a larger customer base of the Healthcare API

Imported from Jira BEAM-10512. Original Jira may contain additional context. Reported by: dranderson@google.com.