Add static maintenance page served by Apache to guides

[pdurbin]

RFI Checklist

1. Related Issues

• Deployment: Create static maintenance page served by Apache until we have read only mode. #2588 Deployment: Create static maintenance page served by Apache until we have read only mode.

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2. Pull Request Checklist

• Functionality completed as described in FRD (no FRD)
• Dependencies, risks, assumptions in FRD addressed (no FRD)
• Unit tests completed (none)
• Deployment requirements identified (e.g., SQL scripts, indexing) (none)
• Documentation completed
• All code checkins completed

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3. Review Checklist

After the pull request has been submitted, fill out this section.

• Code review completed or waived
• Testing requirements completed
• Usability testing completed or waived
• Support testing completed or waived
• Merged with develop branch and resolved conflicts

This work connects to #2588.

[coveralls]

Coverage remained the same at 8.582% when pulling e8d19b3 on 2588-maintenance-pg into be72759 on develop.

[coveralls]

Coverage remained the same at 8.583% when pulling bc21c6f on 2588-maintenance-pg into d601f27 on develop.