typescript-nestjs: queryParameters need to be a URLSearchParameter in order to work

Created by: danielbrammertz

The generated *.service.ts files did not compile when query-parameters with isCollectionFormatMulti=true It produced errors in the following way:

ERROR in ./generated_sources/finapi/access-service/api/transactions.service.ts 478:33-39
TS2339: Property 'append' does not exist on type '{}'.
    476 |         if (order) {
    477 |             order.forEach((element) => {
  > 478 |                 queryParameters.append('order', <any>element);
        |                                 ^^^^^^
    479 |             })
    480 |         }
    481 |

This was fixed, by making queryParameters an instance of URLSearchParam instead of a plain object. Furthermore it turned out, that for regular (non-multi) parameters it is also necessary to append them to URLSearchParam, since the parameters were not sent otherwise

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