v8.5.6 dashboard: Add note about prepared statements in Slow Query Detail (#21375)#21376

ti-chi-bot[bot] merged 1 commit intopingcap:release-8.5pingcap/docs-cn:release-8.5from

ti-chi-bot:cherry-pick-21375-to-release-8.5ti-chi-bot/docs-cn:cherry-pick-21375-to-release-8.5Copy head branch name to clipboard