ZDM-602, ZDM-614, ZDM-583, ZDM-576, DOC-5267, and more - Grab bag of small migration doc updates, old tickets, start detailed cleanup of some topics

[aimurphy]

Grab bag of migration doc updates and old tickets

• ZDM 602: Partially completed in a prior PR. The main request was for a page comparing the tools. I already added this. I made a few changes related to "true zero downtime" vs "some downtime", but I need to work on those pages more generally.
  • Cluster compatibility page
  • Intro > requirements for zero downtime
• ZDM 583: Improve the definitions of ONLY the proxy-level latency metrics, node-level latency metrics, and asynchronous dual reads metrics.
• Add some links to our "Migrate your legacy Cassandra app to Astra DB" webinar.
• Manage proxy instances page:
  • ZDM 614: Add proxy topology addresses section
  • Add and rewrite information about scaling ZDM Proxy instances:
    • Scale with ZDM Proxy Automation
    • Scale ZDM Proxy without Automation
• Troubleshooting:
  • Add troubleshooting tip to query system.peers and system.local
  • Rewrite performance degradation troubleshooting
• Connect clients to proxy page:
  • Rewrite the client credentials section.
  • Add information about token-aware routing with ZDM Proxy
  • Rewrite the CQL Shell connection steps, add a paragraph about cql_version compatibility, and specify that passing the SCB will connect directly to the Astra DB database instead of ZDM Proxy.
  • ZDM 576: Expand the IMPORTANT note to further clarify that sample apps should not be used for performance testing or production workload simulation.
• Expand the information about timestamp preservation in CDM and Sideloader:
  • CDM intro
  • CDM with ZDM Proxy
  • CDM important note about timestamps
  • Sideloader overview > create snapshot backups
• Rewrite a few glossary entries, but many are yet to be edited.
• Add some comments for future work on the feasibility-checklists page.
• Improve the explanations of ZDM Proxy read and write handling on the tool comparison page
• Rewrite asynchronous dual reads content:
  • Route reads to target - Async dual reads tip (more edits planned for this page in future)
  • Phase 3 page
• Other small edits/fixes

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[drchung5]

LGTM