[RFE]Ability to customize prompt when the service is up and running

[yangcao77]

Is your feature request related to a problem? Please describe.
Currently prompt Messages is being referenced as a library import, and cannot be customized once an image is built. It has to be configured properly before the image build.

Describe the solution you'd like
Should allow road-core image consumers to provide their own customized prompt when running the image container, i.e. create an API to change the system prompt

Describe alternatives you've considered

via config to provide customized prompt file path when start the road-core service

Additional context
Add any other context or screenshots about the feature request here.