feat: allow change prompts via django admin

[Henrrypg]

This pull request introduces support for custom system prompts in the AI extensions processors, allowing for greater flexibility when configuring prompt behavior. The main changes ensure that a custom prompt, if provided in the configuration, is used in place of the default system role in relevant API calls.

Custom Prompt Handling:

• Added a custom_prompt attribute to the litellm_base_processor.py class, initialized from the configuration if present.

Prompt Usage in API Calls:

• Updated _build_response_api_params in llm_processor.py to use self.custom_prompt as the system prompt if it exists, otherwise defaulting to the original system_role.
• Updated _call_completion_wrapper in llm_processor.py to use self.custom_prompt as the system prompt if it exists, otherwise defaulting to the original system_role.

How to test

You can setup prompt in LLMProcessor or EducatorAssistantProcessor via AIWorkflowProfile overrides

[openedx-webhooks]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.09%. Comparing base (c3ea4c2) to head (d03d9d2).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
+ Coverage   89.80%   90.09%   +0.28%     
==========================================
  Files          46       46              
  Lines        4041     4129      +88     
  Branches      264      266       +2     
==========================================
+ Hits         3629     3720      +91     
+ Misses        321      320       -1     
+ Partials       91       89       -2     

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[felipemontoya]

Simple and efective.

Combining this with the flexibility of json5 is fantastic.

The one thing I would like is to add a new base template for this. I would call it base.box_custom_prompt

{
  "orchestrator_class": "DirectLLMResponse",
  "processor_config": {
    "LLMProcessor": {
      "stream": true,
      "prompt": "\
You are an educational assistant embedded in an online course. \
 \
Rephrase the given content using different wording while preserving the original meaning, intent, and factual accuracy. \
 \
Guidelines: \
- Do not add new information. \
- Do not remove important details. \
- Do not simplify unless explicitly asked. \
- Keep the length roughly similar to the original. \
- Use clear, natural language suitable for the course audience. \
- Avoid repeating sentence structures or phrases from the original text. \
 \
Output only the rephrased content. \
",
    }
  },
}

[felipemontoya]

Thank you @Henrrypg for taking charge of the QA for this PR