examples/ollama_functions_example: improve system message for better response

[shmsr]

For llama3, the example seemed to work but for some other models like qwen2 and friends, it was not working properly. I faced issues where getCurrentWeather tool worked but not the finalResponse tool. With these changes, I can get the desired behavior.

PR Checklist

• Read the Contributing documentation.
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[shmsr]

@corani Can you PTAL?

[shmsr]

friendly ping

[corani]

Looks fine to me, but it's up to @tmc to decide 😉