feat(ui): add Slack app integration for MaxKB app

[guqing]

What this PR does / why we need it?

支持在 Slack 应用中访问 MaxKB 应用以对接知识库和 AI 问答功能，需要专业版才能使用，此 PR 仅增加了相关 UI 的改动

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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