Upgrade terraform provider `ec`to `0.6.0`.

## Description

A newer version of the Elastic Cloud (`ec`) provider has been released. To make sure we're up to date with all the goodies, we should make the necessary changes that were introduced in 0.6.0 and that are breaking. In Practice there shouldn't be many differences but it may be necessary to explicitly declare topologies in the Elasticsearch block and change the sub-blocks from `elasticsearch {}` to `elasticsearch = {}`, etc.

## Related links

- https://github.com/elastic/terraform-provider-ec/blob/master/CHANGELOG.md#060-feb-28-2023
- #10403 was introduced as a stop-gap measure.