Total count JobExecution matched by query

**Description**  
Add a way to fetch total count `JobExecution` matched by a `Yokai\Batch\Storage\Query`

**Example**  
Add to the `Yokai\Batch\Storage\QueryableJobExecutionStorageInterface`, a method that:
- accept a `Yokai\Batch\Storage\Query` argument 
- return the total `JobExecution` matched by the query