[Website]: Expand / Clarify the support matrix between ESF and Elasticsearch

### Type of issue

None

### What documentation page is affected

https://www.elastic.co/docs/reference/aws-forwarder

### What happened?

The page mentions ESF Elasticsearch output supports ES 7.17.x onwards.

Can we expand the section to at least cover the last major versions (8.x, 9.x) and ideally add a back-reference to this page from https://www.elastic.co/support/matrix

According to the code, it's using the ES Client `elasticsearch==7.17.12` and I do not expect it to use anything fancy apart from the `_bulk`.

### Additional info

This item has to be reviewed by @bturquet & @mlunadia