chore: import upstream snapshot with attribution

docs-website/docs/pipeline-components/joiners/stringjoiner.mdx

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+---
+title: "StringJoiner"
+id: stringjoiner
+slug: "/stringjoiner"
+description: "Component to join strings from different components into a list of strings."
+---
+
+# StringJoiner
+
+Component to join strings from different components into a list of strings.
+
+<div className="key-value-table">
+
+|  |  |
+| --- | --- |
+| **Most common position in a pipeline** | After at least two other components to join their strings                                       |
+| **Mandatory run variables**            | `strings`: Multiple strings from connected components.                                          |
+| **Output variables**                   | `strings`: A list of merged strings                                                             |
+| **API reference**                      | [Joiners](/reference/joiners-api)                                                                      |
+| **GitHub link**                        | https://github.com/deepset-ai/haystack/blob/main/haystack/components/joiners/string_joiner.py |
+| **Package name** | `haystack-ai` |
+
+</div>
+
+## Overview
+
+The `StringJoiner` component collects multiple string outputs from various pipeline components and combines them into a single list. This is useful when you need to merge several strings from different parts of a pipeline into a unified output.
+
+## Usage
+
+```python
+from haystack.components.joiners import StringJoiner
+from haystack.components.builders import PromptBuilder
+from haystack.core.pipeline import Pipeline
+
+string_1 = "What's Natural Language Processing?"
+string_2 = "What is life?"
+
+pipeline = Pipeline()
+pipeline.add_component("prompt_builder_1", PromptBuilder("Builder 1: {{query}}"))
+pipeline.add_component("prompt_builder_2", PromptBuilder("Builder 2: {{query}}"))
+pipeline.add_component("string_joiner", StringJoiner())
+
+pipeline.connect("prompt_builder_1.prompt", "string_joiner.strings")
+pipeline.connect("prompt_builder_2.prompt", "string_joiner.strings")
+
+result = pipeline.run(
+    data={
+        "prompt_builder_1": {"query": string_1},
+        "prompt_builder_2": {"query": string_2},
+    },
+)
+
+print(result)
+```