fix: qna section display errs

[alanlong9278]

Description

Bug 1

• Display: Create new kb from scratch after created from url, the url Kb last qna pair will show in the new kb qna pair when adding new pair.
  
• Reason: the new qna pair index is not match the selected qna group
• Solution: set the qna pair index as the selected qna group's startIndex

Bug 2

• Display: Create new qna pair failed after delete empty qna pair.
  
• Reason: the empty qna pair is not deleted but set isCreateQnaSection as false when clicking delete button, so the updateQnaSection is invoked when re-create the qna pair, but the sectionId is none. The action will trigger the error modal.
• Solution: delete the empty qna pair.

Expected

Task Item

closes #6657

Screenshots

[coveralls]

Coverage decreased (-0.0003%) to 51.4% when pulling 6cd3417 on julong/qna-bugfix into 31d4ca5 on main.