Add a toggle for the iga identity check

Since we may not want to enable the identity check, it must be togglable. This commit adds environment variable REACT_APP_ENABLE_IGA_CHECK for toggling the check in the frontend, and django settings variable IGA_CHECK for toggling the check in the backend.

frontend/src/components/identityLine/index.tsx

@@ -7,6 +7,7 @@ import CheckIcon from '@mui/icons-material/Check'
 import { Trans, useTranslation } from 'react-i18next'
 import { TableCell } from 'components/table'
 import { appInst, disableNinVerification, enableIgaCheck } from 'appConfig'
+
 interface IdentityLineProps {
   text: string
   identity: Identity | null