Improve User Guides

• VTTablet modes should be multiple Guides (Use Vitess with externally Managed MySQL etc)
• VTExplain should be something like "Check Queries for Compatibility"
• Backing Up and Restoring Data is fine (although "Backup and Restore" is shorter)
• Reparenting: Need to think about it, might be multiple guides.
• Topology Service: This is a reference, not a guide
• Transparent Securit Model: This is also a reference
• Upgrading: This is good how it is
• Schema management: might need to be split with some moving to reference. A task guide might be "making schema changes".
  • Create and maintain vindexes user guide.
• Server configuration: might be something like "Configuring Components"

Move summary:

• VTTablet Modes -> Reference
• Topology Service -> Reference
• Transparent Securit Model -> Reference
• Schema Management -> Reference
• VTExplain -> Reference

Summary of next-gen user guides is:

• Production Planning (existing content, but needs editing in #327)
• Configuring Components (maybe eventually production planning can merge here)
• Migrating from MySQL (new content around unmanaged tablets using vreplication workflows)
• Using a Remote/Unmanaged MySQL (new content around Aurora, cloud SQL)
• Unmanaged to Managed Tablets (new content around migration phase 2 using vrepl)
• Multi-cell Deployment #249 (new content)
• Table Migration (currently called Vertical Split. Added in #309, needs to be renamed)
• Horizontal Sharding (will be added in #309)
• Backup and Restore (mostly good how it is)
• Upgrading Vitess (has issues to be fixed in #353 later)
• Validate Query Compatibility (need to write new content around vtexplain)
• Making Schema Changes
• Reparenting (keep as is for now, fix later)
• Integration with Orchestrator (#351)
• Setup TLS https://github.com/vitessio/website/issues/276
• Creating Vindexes
• Configuring VSchema
• Setting up VReplication
• Zookeeper Topology Service
• Consul Topology Service
• Monitoring Vitess

Start with the checklist in this issue and review the existing Vitess user guides and reference pages it names. Use the linked issues #327, #309, #249, #353, #351, and #276 to identify work already covered; done means the guide structure and remaining unchecked topics are updated consistently.