Camel 6137 Send siteCommand(s) without uploading files

CAMEL-6137
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Part 1
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- Added a new option "upload" to the producer which works according to option "download" in the FTP consumer: If false, no file will be uploaded, no temporary file will be created, no done file will be created, but the Exchange.FILE_NAME_PRODUCED header will be set. Defaults to true.
- Since I wanted the "upload" option to work similar as the "download" option, I added an isUploadFile() method to the GenericFileProducer in camel-core. This is the only change in camel-core.

Part 2
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- Added a new option "siteCommandCapture" to the RemoteFileConfiguration: if true, the output of the site commands will be returned in the exchange's body as a List<String> with the output of each executed site command as a list element in order of execution. If false, the body remains untouched. Defaults to false.

The default behaviour remains as before.