Migrate data from OSS v1/v2 to InfluxDB 3 Enterprise

We have a brief about dual writing that suggests using it for migration:
> Use Telegraf to write your data simultaneously to multiple InfluxDB instances or clusters. This method, known as “dual writing,” is useful for backing up data to a separate instance or for migrating from other versions of InfluxDB to InfluxDB 3 Enterprise.
and we have very brief guides for API compatibility.

Add a page that's more explicit about the recommended steps and suggestions for historical data.

[Slack Message](https://influxdata.slack.com/archives/C084G9LR2HL/p1747254090501799?thread_ts=1747246425.951549&cid=C084G9LR2HL)

Start with the linked Telegraf dual-write guide and the existing API compatibility guides, then review the linked Slack discussion for migration context. The new page is done when it documents recommended steps for moving from OSS v1/v2 to InfluxDB 3 Enterprise and gives guidance for migrating historical data.

Written by the indexing model from the issue text.