`get_benchmark`: Unintuitive behavior for mapped layer

[nquetschlich]

Currently, it is not sufficient to only specify the device_name for non-ibm devices when using the get_benchmark method:

get_benchmark(
    benchmark_name: str,
    level: Union[str, int],
    circuit_size: int = None,
    benchmark_instance_name: str = None,
    compiler: str = "qiskit",
    compiler_settings: mqt.bench.CompilerSettings = None,
    gate_set_name: str = "ibm",
    device_name: str = "ibm_washington",
):

If only the device_name is specified, the default gate_set_name value (==ibm) is used, which is unintuitive and, therefore, not ideal. It should be sufficient to only use the device_name as parameter and deduct the respective gate_set_name.

[nquetschlich]

fixed by #272