[DOCS] Tweak doc test to sync_flush
[DOCS] Tweak doc test to sync_flush

The response is attempting to illustrate the sync_id marker, but in
the test the index is too "fresh" to have a sync marker. So the test
needs to execute a sync flush behind the scenes so that the marker
is present

fred84/elasticsearch,shreejay/elasticsearch,nezirus/elasticsearch,mohit/elasticsearch,masaruh/elasticsearch,naveenhooda2000/elasticsearch,pozhidaevak/elasticsearch,gingerwizard/elasticsearch,Stacey-Gammon/elasticsearch,brandonkearby/elasticsearch,qwerty4030/elasticsearch,ThiagoGarciaAlves/elasticsearch,wangtuo/elasticsearch,wangtuo/elasticsearch,umeshdangat/elasticsearch,qwerty4030/elasticsearch,markwalkom/elasticsearch,sneivandt/elasticsearch,uschindler/elasticsearch,masaruh/elasticsearch,pozhidaevak/elasticsearch,ThiagoGarciaAlves/elasticsearch,nezirus/elasticsearch,pozhidaevak/elasticsearch,scottsom/elasticsearch,kalimatas/elasticsearch,wangtuo/elasticsearch,jimczi/elasticsearch,rajanm/elasticsearch,jimczi/elasticsearch,strapdata/elassandra,Stacey-Gammon/elasticsearch,lks21c/elasticsearch,wenpos/elasticsearch,gingerwizard/elasticsearch,strapdata/elassandra,gingerwizard/elasticsearch,mjason3/elasticsearch,nknize/elasticsearch,scottsom/elasticsearch,ThiagoGarciaAlves/elasticsearch,LeoYao/elasticsearch,GlenRSmith/elasticsearch,lks21c/elasticsearch,LeoYao/elasticsearch,vroyer/elasticassandra,LeoYao/elasticsearch,sneivandt/elasticsearch,mjason3/elasticsearch,s1monw/elasticsearch,gfyoung/elasticsearch,brandonkearby/elasticsearch,sneivandt/elasticsearch,kalimatas/elasticsearch,LeoYao/elasticsearch,brandonkearby/elasticsearch,ThiagoGarciaAlves/elasticsearch,GlenRSmith/elasticsearch,kalimatas/elasticsearch,Stacey-Gammon/elasticsearch,nezirus/elasticsearch,vroyer/elassandra,coding0011/elasticsearch,sneivandt/elasticsearch,vroyer/elassandra,rajanm/elasticsearch,fred84/elasticsearch,scorpionvicky/elasticsearch,s1monw/elasticsearch,mjason3/elasticsearch,mjason3/elasticsearch,wangtuo/elasticsearch,strapdata/elassandra,mohit/elasticsearch,nezirus/elasticsearch,rajanm/elasticsearch,umeshdangat/elasticsearch,s1monw/elasticsearch,wangtuo/elasticsearch,qwerty4030/elasticsearch,nezirus/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,markwalkom/elasticsearch,robin13/elasticsearch,maddin2016/elasticsearch,naveenhooda2000/elasticsearch,masaruh/elasticsearch,vroyer/elassandra,kalimatas/elasticsearch,maddin2016/elasticsearch,fred84/elasticsearch,maddin2016/elasticsearch,kalimatas/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,ThiagoGarciaAlves/elasticsearch,shreejay/elasticsearch,HonzaKral/elasticsearch,nknize/elasticsearch,scottsom/elasticsearch,maddin2016/elasticsearch,mohit/elasticsearch,uschindler/elasticsearch,shreejay/elasticsearch,coding0011/elasticsearch,maddin2016/elasticsearch,umeshdangat/elasticsearch,rajanm/elasticsearch,strapdata/elassandra,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,naveenhooda2000/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch,nknize/elasticsearch,scottsom/elasticsearch,scorpionvicky/elasticsearch,mohit/elasticsearch,qwerty4030/elasticsearch,umeshdangat/elasticsearch,pozhidaevak/elasticsearch,gfyoung/elasticsearch,scottsom/elasticsearch,Stacey-Gammon/elasticsearch,LeoYao/elasticsearch,mohit/elasticsearch,scorpionvicky/elasticsearch,masaruh/elasticsearch,LeoYao/elasticsearch,LeoYao/elasticsearch,markwalkom/elasticsearch,uschindler/elasticsearch,naveenhooda2000/elasticsearch,fred84/elasticsearch,coding0011/elasticsearch,gfyoung/elasticsearch,markwalkom/elasticsearch,gingerwizard/elasticsearch,wenpos/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,HonzaKral/elasticsearch,jimczi/elasticsearch,jimczi/elasticsearch,lks21c/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,wenpos/elasticsearch,gfyoung/elasticsearch,fred84/elasticsearch,umeshdangat/elasticsearch,shreejay/elasticsearch,ThiagoGarciaAlves/elasticsearch,wenpos/elasticsearch,strapdata/elassandra,GlenRSmith/elasticsearch,rajanm/elasticsearch,Stacey-Gammon/elasticsearch,markwalkom/elasticsearch,brandonkearby/elasticsearch,lks21c/elasticsearch,sneivandt/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,rajanm/elasticsearch,pozhidaevak/elasticsearch,s1monw/elasticsearch,wenpos/elasticsearch,coding0011/elasticsearch,jimczi/elasticsearch,GlenRSmith/elasticsearch,lks21c/elasticsearch,s1monw/elasticsearch,gingerwizard/elasticsearch,markwalkom/elasticsearch,mjason3/elasticsearch,vroyer/elasticassandra,qwerty4030/elasticsearch,nknize/elasticsearch,masaruh/elasticsearch,vroyer/elasticassandra,uschindler/elasticsearch,naveenhooda2000/elasticsearch,brandonkearby/elasticsearch,shreejay/elasticsearch