Clarify that `insert_overwrite` strategy is not supported by Iceberg table for dbt-athena

### Contributions

- [x] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

https://docs.getdbt.com/reference/resource-configs/athena-configs#incremental-models

### What part(s) of the page would you like to see updated?

In the page above, both sections "supported incremental models" and "limitation when using Iceberg models" currently do not clarify that the `insert_overwrite` incremental model is NOT supported by DBT Athena with Iceberg tables. I believe this is a mistake as the `dbt-athena` adapter will only allow `append`, `microbatch`, and `merge` strategy for Iceberg tables. See below for reference.

The docs should transparently clarify this fact about Iceberg models, the same way that:
- the limitation of "Sync all columns on schema change" is mentioned
- the limitation of `merge` strategy being available only on Iceberg tables is mentioned

### Additional information

In the adapter's README, support for `insert_overwrite` is only mentioned under Hive tables (and not Iceberg) which I believe is intended:
https://github.com/dbt-labs/dbt-adapters/tree/main/dbt-athena#features

I received this error message when attempting to use `insert_overwrite` on my Iceberg table: https://github.com/dbt-labs/dbt-adapters/blob/main/dbt-athena/src/dbt/include/athena/macros/materializations/models/incremental/helpers.sql#L5

I'd be willing to PR this if needed, please let me know.