Add EKS CI to new GA test workflow

[moukoublen]

After implementing the https://github.com/elastic/cloudbeat/issues/1976 of GA testing workflows (https://github.com/elastic/cloudbeat/pull/2000), EKS ci should be add to it and marked with if: ${{ !contains(fromJSON('["pull_request_target", "pull_request"]'), github.event_name) }} to run only after merge or on-demand.