Describe the bug
The DocumentJoiner component's run method doesn't allow you to pass a value for the top_k parameter, see here. If you try to do so, you'll get the following: ValueError: Input top_k not found in component joiner.

This means you can only pass a value for top_k when you initialize the component, and so you can't give it a value e.g. at query time using pipe.run("DocumentJoiner": {"top_k": top_k}) if you use it in a query pipeline.

Expected behavior
Providing this component with a top_k value in a pipeline using e.g. pipe.run("DocumentJoiner": {"top_k": top_k}) should not raise a ValueError.

A simple change to the run method, adding top_k as an argument, and replacing these lines inside the function with the following should fix it:

if top_k:
    output_documents = output_documents[: top_k]
elif self.top_k:
    output_documents = output_documents[: self.top_k]

To Reproduce
Create a query pipeline containing a DocumentJoiner and run it using pipe.run("DocumentJoiner": {"top_k": top_k}).

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