[Task] Fully support requirement suggestion

[malusamayo]

We currently use mock-up code for requirement suggestion. Replace it with LLM-based suggestion.

For the suggestion, sample 5 input/output pairs (if output is not available, just use inputs) for LLM to look at.

Once the backend is complete, trigger requirement suggestions after prompt updates / run.

[cassandrashi]

pushed the code to dev branch

[malusamayo]

One additional feature we can add:

• For each suggested requirement, ask LLM to output a related example, and also add the example to the requirement