docstr: Take strings from multiple input nodes and join them
  into a single one returned in output. Since `input_str`
  is Variadic, we know we'll receive a List[str].
code: def run(self, input_str: Variadic[str]):
      """
      Take strings from multiple input nodes and join them
      into a single one returned in output. Since `input_str`
      is Variadic, we know we'll receive a List[str].
      """
      return {"output": " ".join(input_str)}
  
file_path: haystack/haystack/testing/sample_components/joiner.py
imports: from typing import List
  from haystack.core.component import component
  from haystack.core.component.types import Variadic
label_desc: Use image node_id 1 for calling the StringJoiner obj's underlying member method code with example usage: obj.run(input_str) and returns: dict