provide an option to select transport

[ffang]

currently in the generated camel-context.xml, the jetty transport is used like

<restConfiguration component="jetty" host="localhost" port="8080" bindingMode="json">
        </restConfiguration>

Would be handy to provide an option so that we can select which transport whe want to use for Rest DSL(undertow/servlet, etc)
like

<restConfiguration component="servlet" host="localhost" port="8080" bindingMode="auto">
        </restConfiguration>