Rework prompt examples system

[nsarrazin]

Describe your feature request

Currently we store simple prompts under each model. This is annoying since we have to manually add them to each model each time.

It also only supports simple text prompts. We could replace this by a list of prompt examples that have different requirements (multimodal, tool use, etc.) and sample valid prompts on page load. We could use this to highlight tool use, multimodal models, etc.

Implementation idea

Add an env variable for PROMPT_EXAMPLES and make it an array with prompts. Optionally add fileUrl or toolId as well to specify if a file should be passed to the model or if a tool should be active when calling this example. Sample some valid examples in the UI on the chat introduction component.