Implement a logic that synchronizes sync source with oplog_global

Implement integration tests:
Test1:
insert document D1 to S1
verify its inserted to a global_oplog
verify its migrated to S2 and S3 oplog
verify its applied on S2 and S3

Test2:
insert 2 documents to S1
verify they inserted to a global_oplog
verify they migrated to S2 and S3 oplog
verify they applied on S2 and S3