Decode based on column names

[gwils]

Add the ability to decode a field based on its name as found in the header, to complement the current position-based decoding.

[ghost]

Example usage https://github.com/databrary/databrary/blob/kanishka-dbd-845-b2/src/Databrary/Model/Ingest.hs#L373 , pasted inline:

participantRecordParseNamedRecord :: ParticipantFieldMapping -> Csv.NamedRecord -> Parser ParticipantRecord
participantRecordParseNamedRecord fieldMap m = do
    mId <- extractIfUsed2 pfmId validateParticipantId
    mInfo <- extractIfUsed2 pfmInfo validateParticipantInfo
    mDescription <- extractIfUsed2 pfmDescription validateParticipantDescription
    mBirthdate <- extractIfUsed2 pfmBirthdate validateParticipantBirthdate
    mGender <- extractIfUsed2 pfmGender validateParticipantGender
    mRace <- extractIfUsed2 pfmRace validateParticipantRace
    mEthnicity <- extractIfUsed2 pfmEthnicity validateParticipantEthnicity
    mGestationalAge <- extractIfUsed2 pfmGestationalAge validateParticipantGestationalAge
    mPregnancyTerm <- extractIfUsed2 pfmPregnancyTerm validateParticipantPregnancyTerm
    mBirthWeight <- extractIfUsed2 pfmBirthWeight validateParticipantBirthWeight
    mDisability <- extractIfUsed2 pfmDisability validateParticipantDisability
    mLanguage <- extractIfUsed2 pfmLanguage validateParticipantLanguage
    mCountry <- extractIfUsed2 pfmCountry validateParticipantCountry
    mState <- extractIfUsed2 pfmState validateParticipantState
    mSetting <- extractIfUsed2 pfmSetting validateParticipantSetting
    pure
        (ParticipantRecord
            { prdId = mId
            , prdInfo = mInfo
            , prdDescription = mDescription
            , prdBirthdate = mBirthdate
            , prdGender = mGender
            , prdRace = mRace
            , prdEthnicity = mEthnicity
            , prdGestationalAge = mGestationalAge
            , prdPregnancyTerm = mPregnancyTerm
            , prdBirthWeight = mBirthWeight
            , prdDisability = mDisability
            , prdLanguage = mLanguage
            , prdCountry = mCountry
            , prdState = mState
            , prdSetting = mSetting
            } )
  where
    extractIfUsed2
      :: (ParticipantFieldMapping -> Maybe Text) -> (BS.ByteString -> Maybe BS.ByteString) -> Parser (Maybe BS.ByteString)
    extractIfUsed2 maybeGetField validateValue = do
        case maybeGetField fieldMap of
            Just colName -> do
                contents <- m .: (TE.encodeUtf8 colName)
                maybe
                    (fail ("invalid value for " ++ show colName ++ ", found " ++ show contents))
                    (pure . Just)
                    (validateValue contents)
            Nothing ->
                pure Nothing