Add write-data guides and best practices for InfluxDB 3 Cloud

Cloud pages don't exist yet at the paths below, so content/influxdb3/cloud/request-information.md aliases them to a "Request more information" page. Publish the real content and remove the alias.

Closest existing equivalent to source from: /influxdb3/enterprise/write-data/

Aliased paths

• /influxdb3/cloud/write-data/best-practices/optimize-writes/
• /influxdb3/cloud/write-data/best-practices/schema-design/
• /influxdb3/cloud/write-data/use-telegraf/
• /influxdb3/cloud/write-data/use-telegraf/csv/

Anchors the new content must provide

Shared content deep-links to these fragments. They're currently faked as hidden <span>s in request-information.md; remove each span once the real heading exists.

• #avoid-wide-schemas
• #design-for-performance
• #sort-tags-by-query-priority

Done when

• Content is published (or the linking shared content is gated for Cloud)
• The alias is removed from request-information.md
• Any hidden anchor <span>s that belonged to these paths are removed
• link-checker passes

Part of #7391.

Start with the existing /influxdb3/enterprise/write-data/ content and inspect content/influxdb3/cloud/request-information.md for the aliases and hidden anchor spans. Create the four Cloud write-data pages with the required fragments, remove the alias and obsolete spans, and run link-checker. Done means the content or gated links work and link-checker passes.