[AWS] lastSync option of start_position parameter not available in stack version before 8.19.0

Coming from [SDH](https://github.com/elastic/sdh-beats/issues/6706). 
Details for the problem and solution can be found in https://github.com/elastic/sdh-beats/issues/6706#issuecomment-3616286282 and https://github.com/elastic/sdh-beats/issues/6706#issuecomment-3616705678

Useful link: 
https://www.elastic.co/docs/extend/integrations/developer-workflow-support-old-package