Change the role to "user" in format function of ollama chat model

[zhijianma]

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name: Pull Request about: Create a pull request

Description

[Please describe the background, purpose, changes made, and how to test this PR] According to issue #441 Change role from system to user

Checklist

Please check the following items before code is ready to be reviewed.

• [x] Code has passed all tests
• [x] Docstrings have been added/updated in Google Style
• [x] Documentation has been updated
• [x] Code is ready for review