Allow system prompt override for dev

[TamiTakamiya]

Description

This is the implementation of Issue #158:

• A new optional string parameter system_prompt is added to the /v1/query endpoint.
• System prompt override occurs only when dev_config.enable_system_prompt_override is set to true.
  • Default is false.
  • When dev_config.enable_system_prompt_override is set to false and /v1/query is invoked with system_prompt, the value specified in system_prompt is ignored.
• Gradio UI is updated for specifying system_prompt for debug UI. See the video attached to [RFE] Allow to override system prompt in "debug" mode #158.

Type of change

• Refactor
• New feature
• Bug fix
• CVE fix
• Optimization
• Documentation Update
• Configuration Update
• Bump-up dependent library
• Bump-up library or tool used for development (does not change the final image)
• CI configuration change
• Konflux configuration change

Related Tickets & Documents

• Related Issue # n/a
• Closes # n/a

Checklist before requesting a review

• I have performed a self-review of my code.
• PR has passed all pre-merge test jobs.
• If it is a core feature, I have added thorough tests.

Testing

• Please provide detailed steps to perform tests related to this code change.
• How were the fix/results from this change verified? Please provide relevant screenshots or results.

[tisnik]

it looks ok, glad you updated Gradio UI as well