[Bug] Improve errors in evaluation view

[mmabrouk]

When errors happen in the evaluation view, there are a couple of problems:

• The error in the llm app are shown in black and not in red as expected
• The error in the llm app is very general (500 internal error) and does not provide details about the message in the error as we do have in the playground (❌ Model gpt-3.5-turbo does not support JSON response format)
• The error for the evaluation is the same as in the llm app. Instead we should say "LLM app failed" or something similar.