Add ability to configure prefix for the add.fields and add.headers

Currently Debezium always add "__" as the prefix for the fields and headers. 

When we use camel kafka connector (especially for the headers) we must prefix the header with "CamelHeader.". Else these are not getting added to the message.

We need to add support in the io.debezium.transforms.ExtractNewRecordState

• "add.fields.prefix" -> String with the default value of "__"
• "add.headers.prefix" -> String with the default value of  "__". 

When it is there like this for camel kafka connector, we can set the configuration "add.headers.prefix" to "CamelHeader."