Using anchors and aliases in Pipeline YAML

[julian-risch]

Is your feature request related to a problem? Please describe.
ChatGenerators and ToolInvokers both have a tools parameter and in many pipelines, the tools parameter can be set to the same object: the same tool/list of tools.

Describe the solution you'd like
We should investigate if and how anchors and aliases can be used in Haystack pipelines.

• Check if a pipeline yaml with manually added anchors and aliases can be loaded correctly
• Investigate when the YamlDumper makes use of anchors and aliases
• Document the findings, for example extending https://docs.haystack.deepset.ai/docs/serialization

Example without anchors and aliases
Simple pipeline with tools based on cookbook.

Pipeline 1

```yaml components: generator: init_parameters: api_base_url: null api_key: env_vars: - OPENAI_API_KEY strict: true type: env_var generation_kwargs: {} max_retries: null model: gpt-4o-mini organization: null streaming_callback: null timeout: null tools: - description: A tool to get the weather function: __main__.dummy_weather name: weather parameters: properties: location: type: string required: - location type: object tools_strict: false type: haystack.components.generators.chat.openai.OpenAIChatGenerator router: init_parameters: custom_filters: {} optional_variables: [] routes: - condition: '{{replies[0].tool_calls | length > 0}}' output: '{{replies}}' output_name: there_are_tool_calls output_type: typing.List[haystack.dataclasses.chat_message.ChatMessage] - condition: '{{replies[0].tool_calls | length == 0}}' output: '{{replies}}' output_name: final_replies output_type: typing.List[haystack.dataclasses.chat_message.ChatMessage] unsafe: true validate_output_type: false type: haystack.components.routers.conditional_router.ConditionalRouter tool_invoker: init_parameters: convert_result_to_json_string: false raise_on_failure: true tools: - description: A tool to get the weather function: __main__.dummy_weather name: weather parameters: properties: location: type: string required: - location type: object type: haystack.components.tools.tool_invoker.ToolInvoker connections: - receiver: router.replies sender: generator.replies - receiver: tool_invoker.messages sender: router.there_are_tool_calls max_runs_per_component: 100 metadata: {} ```

Example with anchors and aliases
Note how *id001 is used for the tools parameter of ToolInvoker instead of redefining what was already used for the tools parameter of the OpenAIChatGenerator under &id001

Pipeline 2

```yaml components: generator: init_parameters: api_base_url: null api_key: env_vars: - OPENAI_API_KEY strict: true type: env_var generation_kwargs: {} max_retries: null model: gpt-4o-mini organization: null streaming_callback: null timeout: null tools: &id001 - description: A tool to get the weather function: __main__.dummy_weather name: weather parameters: properties: location: type: string required: - location type: object tools_strict: false type: haystack.components.generators.chat.openai.OpenAIChatGenerator router: init_parameters: custom_filters: {} optional_variables: [] routes: - condition: '{{replies[0].tool_calls | length > 0}}' output: '{{replies}}' output_name: there_are_tool_calls output_type: typing.List[haystack.dataclasses.chat_message.ChatMessage] - condition: '{{replies[0].tool_calls | length == 0}}' output: '{{replies}}' output_name: final_replies output_type: typing.List[haystack.dataclasses.chat_message.ChatMessage] unsafe: true validate_output_type: false type: haystack.components.routers.conditional_router.ConditionalRouter tool_invoker: init_parameters: convert_result_to_json_string: false raise_on_failure: true tools: *id001 type: haystack.components.tools.tool_invoker.ToolInvoker connections: - receiver: router.replies sender: generator.replies - receiver: tool_invoker.messages sender: router.there_are_tool_calls max_runs_per_component: 100 metadata: {} ```