Feature/get current credit limit

this
```
->filterByBorrower($borrower)
->filterByDeletedByAdmin(false)
->filterByStatus(Loan::REPAID)
->filterByExpiredAt(null)
->select('AmountRaised')
->withColumn('MAX(raised_usd_amount)', 'AmountRaised')
```

is exactly the same as a couple of lines above, refactor this