docs: DOC-912: Add Maintenance Mode Documentation

[achuribooks]

Describe the Change

This PR fills a documentation hole pertaining to maintenance mode, which was implemented in 4.0 but never documented outside of release notes. Existing release notes are also misleading, as maintenance mode also works on non-VMO clusters.

PR 5193 fixes the release note. Merge it ONLY AFTER this PR (5100) is complete.

Changed Pages

💻

• Maintenance Mode - Created new page.
• Manage Clusters - Added to bottom of page as a bullet.
• Create Cluster Backup - Limitation added.
• Compliance Scan - Updated note to indicate that scans cannot be performed in maintenance mode.
• Architecture - Added x-ref to new maintenance mode page.
• Migrate a VM to a Different Node - Added x-ref to new maintenance mode page.

Jira Tickets

🎫 DOC-912

Backports

Can this PR be backported?

• Yes. Remember to add the relevant backport labels to your PR.
• No. Please leave a short comment below about why this PR cannot be backported.

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[karl-cardenas-coding]

@achuribooks this needs to follow our how-to layout. Assume the reader freshly logged into Palette, and has no idea how to get to this feature.