Add ClickUp integration documentation

[codegen-sh]

This PR adds documentation for the ClickUp integration, similar to the existing Linear integration documentation. The changes include:

1. Created a new clickup.mdx file in the docs/integrations directory with comprehensive documentation on the ClickUp integration
2. Added ClickUp to the navigation in docs.json
3. Added ClickUp to the capabilities overview in capabilities.mdx
4. Added ClickUp to the interrupts documentation in interrupts.mdx
5. Added ClickUp to the agent permissions documentation in agent-permissions.mdx
6. Added ClickUp to the overview page in overview.mdx
7. Added a placeholder for the ClickUp image

Note: The actual ClickUp image needs to be added to replace the placeholder file at docs/images/clickup.png.placeholder.

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💻 View my work • 👤 Initiated by @kopekC • About Codegen
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.