Pdi 10878 - Synchronize after merge step error: "savepoint is not valid for this transaction" for MS SQL Server and error handling

What was done:
1) Introduced supportsSavepoints flag which is checked in all the places where we try to create save point
2) Added special exception handling for the case when we try to rollback to null savepoint. This happens when look up failure occurred
3) Added Unit test for the issue