fix CAMEL-7450: CsvDataFormat unable to setup header when useMaps=true

https://issues.apache.org/jira/browse/CAMEL-7450

Hi all,
seems that it is impossible to setup the header of a csv when using a map.
It is always used the first line of the CSV file.
Using this configuration in conjunction with my patch I'm currently able to do so (also having the skipFirstLine flag working with useMaps="true")
Configuration:
https://github.com/ccancellieri/camel_poc/blob/master/src/main/resources/META-INF/spring/camel-context.xml

Is this acceptable for you?