add checkpoint sync file timestress 

The __wt_btree_syncing_by_other_session function will affect reconcile. The longer __wt_sync_file() takes, the greater the impact __wt_btree_syncing_by_other_session. For example, a big page is generated, which takes a long time to execute and causes service jitter(Submit the code in another PR).

Add checkpoint_sync_file to simulate service jitter caused by slow checkpoint_sync_file .