Can't update start user id for historic process instance

**Describe the bug**
Can't update start user id for historic process instance.
I checked the mybatis mapping xml for historicProcessInstance, there is no update sql for start user id. We need to update the start user id to null when the user need to be off boarding.

**Expected behavior**
The start user id can be updated.

**Code**
HistoricProcessInstanceEntityManager historicProcessInstanceEntityManager =
CommandContextUtil.getHistoricProcessInstanceEntityManager();
List processInstanceList =
historicProcessInstanceEntityManager.findHistoricProcessInstancesByQueryCriteria(historicProcessInstanceQuery);
for (HistoricProcessInstance processInstance : processInstanceList) {
HistoricProcessInstanceEntity processEntity = (HistoricProcessInstanceEntity) processInstance;
processEntity.setStartUserId(null);
historicProcessInstanceEntityManager.update(processEntity);
}

**Additional context**
Flowable version: 6.4.2
Database: postgresql 11