feat: provide kafka-broker transfer streaming sample

[ndr-brt]

What this PR changes/adds

Adds a streaming kafka-broker sample, that shows how to stream data through EDC with a custom DataFlowController without using the data-plane.

Why it does that

streaming

Further notes

• removed the Checkstyle job in the ci as Build already runs checkstyle
• cleanup FileTransferCommon, that contained a lot of unused methods

Linked Issue(s)

Closes #150

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[bscholtes1A]

This is awesome!
Small question though, could the set of .json files be replaced by a Postman collection?
The advantage is that the placeholder values can be set as collection variables.

Also doing so it is possible to automate the process of extracting the value from a response to set a variable for the next request .

[ndr-brt]

This is awesome! Small question though, could the set of .json files be replaced by a Postman collection? The advantage is that the placeholder values can be set as collection variables.

Also doing so it is possible to automate the process of extracting the value from a response to set a variable for the next request .

currently all the samples work with json files, because they can be used both in the sample manual process and in the automated tests. The postman thing could be proposed in a new issue eventually