refactor: params to plan prompt

[jmatejcz]

Purpose

• Parametrize Megamind plan prompt

Proposed Changes

PlanPrompts dataclass

Issues

• Links to relevant issues

Testing

Test it out with some random prompts in file rai_bench/examples/tool_calling_custom_agent.py

prompts = PlanPrompts(
        objective_template="xddddd\n",
        first_step_prompt="\ndo first step!!!\n",
        steps_done_header="Bly bly bly:\n",
        next_step_prompt="do somth lol: \n",
        completion_prompt="return when finished",
    )

  agent = create_megamind(
      megamind_llm=supervisor_llm,
      megamind_system_prompt=task.get_system_prompt(),
      executors=executors,
      anylyzer_prompt=task.get_planning_prompt(),
      plan_prompts=prompts,
  )

You should see difference in user prompt