New doc onboard: Zebra documentation

[nannanli]

Zebra is an incubator project now. This issue tracks its documentation delivery on the Zowe doc site.

Its documentation is now hosted in the GitHub repo: https://github.com/zowe/zebra/tree/main/Documentation

[nannanli]

To add a set of documentation for Zebra, consider updating the following locations:

• Provide a brief introduction to ZABRA in the overview section: https://docs.zowe.org/stable/getting-started/overview/#component-overview (Source files stored in /docs/getting-started)
• If you have a quick start guide, add it to the Zowe quick start section. For example: https://docs.zowe.org/stable/getting-started/cli-getting-started (Source files stored in /docs/getting-started)
• Anything about installing and using ZABRA can be added to the User Guide section as a new chapter similar to Zowe Explorer: https://docs.zowe.org/stable/user-guide/ze-install (Source files stored in /docs/user-guide)
• Anything about developing for ZABRA can be added to the Extending section (Source files stored in /docs/extend)
• Similarly, anything about troubleshooting ZABRA can be added to the Troubleshooting section (Source files stored in /docs/troubleshoot)
• If you have any API reference information, you can add it to the Reference section (Source files stored in /docs/appendix)

To update the left-hand navigation tree, update the file docs/sidebar.js.

Please assign @nannanli as a reviewer once the PR is ready or contact me for any further questions. Thank you!