@Override
  public QuotaSource getQuotaSource() {
    return ambryCUQuotaSource;
  }
Constructor for {@link AmbryCUQuotaSourceFactory}.
@param quotaConfig {@link QuotaConfig} object.
@param accountService {@link AccountService} object.
@param quotaMetrics {@link QuotaMetrics} object.
@param routerConfig {@link RouterConfig} object.
ambry-quota/src/main/java/com/github/ambry/quota/capacityunit/AmbryCUQuotaSourceFactory.java