Rename the system parameter to system_prompt for clarity

[dpoulopoulos]

The system parameter we use in-place of system_prompt when making inference requests (see here) is ambiguous and could be confused with other system-related functionalities. To improve clarity and maintain consistency, we should rename it to system_prompt.

Tasks:

• Identify all occurrences of system used as a parameter.
• Refactor system to system_prompt across the codebase.
• Consider providing a deprecation warning if this is a breaking change.
• Update related documentation, comments, and examples.
• Ensure all tests pass after the refactor.