Move FragmentInstanceExecStatus' AuxErrorInfo to StatefulStatus

Surfaced by twmarshall in IMPALA-9295:

If the report where the AuxErrorInfoPB is sent is dropped/fails, eg. due to backpressure at the coordinator or a flaky network, the next report won't contain the AuxErrorInfoPB, it will just be dropped.

Fortunately, we already dealt with this situation for the error log and you just need to do the same thing as we did there, i.e. move AuxErrorInfoPB into the StatefulStatusPB