Add internals reference (data retention, durability) for InfluxDB 3 Cloud

Cloud pages don't exist yet at the paths below, so [`content/influxdb3/cloud/request-information.md`](https://github.com/influxdata/docs-v2/blob/master/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/reference/internals/`

## Aliased paths

- [ ] `/influxdb3/cloud/reference/internals/data-retention/`
- [ ] `/influxdb3/cloud/reference/internals/durability/`

## Anchors the new content must provide

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

- `#retention-period-precedence`

## 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 ``s that belonged to these paths are removed
- [ ] `link-checker` passes

Part of #7391.

Start by comparing /influxdb3/enterprise/reference/internals/ with the requested Cloud data-retention and durability paths, then inspect content/influxdb3/cloud/request-information.md for the aliases and hidden anchors. Publish the corresponding Cloud content, remove the alias and relevant spans, and verify that link-checker passes.

Written by the indexing model from the issue text.