Extend CLI to support usage of a generic agent via Docker image and customizable start command

[nezhar]

Goal

Allow users to flexibly define and run a generic agent with the CLI by specifying a Docker image and a custom start command (or a similar parameter).

Proposed Features

• Add CLI options to:
  • Accept a user-supplied Docker image for the agent
  • Accept a start command or entrypoint to launch the agent inside the specified image
• Ensure the CLI can pass required configuration, volumes or environment variables as needed
• Validate user inputs and provide relevant errors if configuration is missing or incorrect

Why

Supporting generic agents makes the CLI more flexible and adaptable to multiple agent implementations—including private or experimental agents—beyond any hardcoded images.

Acceptance Criteria

• CLI supports new arguments for custom Docker image and start command
• CLI launches agent using these custom parameters
• Proper error messages for invalid or missing parameters
• Documentation (README) updated to explain using the new feature

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Label: enhancement