Add entities for Assist's pipelines

Feature Requests
1

Add entities for Assist’s pipelines, with the ability to retrieve the conversation agent’s value via attributes.
It will help to specify variable agent value in scripts with conversation.process.
Now it is only possible to implement this if you assign identical names for agent and pipeline, which has some limitations

  - action: conversation.process
    metadata: {}
    data:
      agent_id: >-
        {{states.conversation |
        selectattr('attributes.friendly_name','match','^'~states('select.'~device_attr(trigger.device_id,
        "name")~'_assistant')) | map(attribute='entity_id') | first}}
      text: 'What's your opinion of the news: {{news_var}}'
    response_variable: bla

Example use case: there are several HAVPEs in the house, one uses chatGPT, one uses Gemini. Each agent has a personalized promt.
In this configuration, it is possible to call the same script to process the information, but get different outputs.