Allow User for resource_id on chat action

What does this MR do and why?

Allow User for resource_id on chat action

This allows the User to be a resource_id for the aiAction chat input. This is a temporary solution as we want to make resource_id optional. Until we're able to do so, we allow to use the resource to be the current_user.

This is how we also do it for TanukiBot right now.

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Before	After

How to set up and validate locally

1. Set up the local environment for Anthropic https://docs.gitlab.com/ee/development/ai_features.html#test-ai-features-locally
2. Enable the feature flag Feature.enable(:gitlab_duo)
3. Test it with the GraphQL mutation and message history:

# get the messages after submitting the mutation
query messages {
  aiMessages {
    nodes {
      id
      requestId
      content
      errors
      role
    }
  }
}

mutation chat {
  aiAction(input:{chat:{resourceId:"gid://gitlab/User/1", content:"What is the title from the issue http://gdk.test:3000/flightjs/Flight/-/issues/37?"}}) {
    requestId
    errors
  }
}

NOTE: Expectations is not that the chat history will respond with the info yet, this is WIP from another MR.

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