fix(chatMessages): Fix error on answering question

[ZongZiWang]

Description

• Fix chat question endpoint 500 error caused by feat(chatMessages): add brain_id and prompt_id columns  #912
  • Typo on get_brain_prompt_id logic
  • Logging issue at get_default_user_brain
  • Currently not returning the answer from the end point

Fixes #952

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented hard-to-understand areas
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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[StanGirard]

Thanks a lot for the PR !