Support using package-private classes as POJOs for InfluxDBResultMapper

I'm using `org.influxdb:influxdb-java:2.10`.
I'd like to limit my `@Measurement` classes visibility to package-private, but currently it doesn't work because of the following exception:

```
org.influxdb.InfluxDBMapperException: java.lang.IllegalAccessException: Class org.influxdb.impl.InfluxDBResultMapper can not access a member of class com.example.MyMeasurement with modifiers "public"
```

The line which causes this is https://github.com/influxdata/influxdb-java/blob/influxdb-java-2.10/src/main/java/org/influxdb/impl/InfluxDBResultMapper.java#L160.
Looks like it will be enough to replace
```
object = clazz.newInstance();
```

with

```
Constructor defaultConstructor = clazz.getDeclaredConstructor();
defaultConstructor.setAccessible(true);
object = declaredConstructor.newInstance();
```

If there are no objections, I'll provide a PR.

Inizia in src/main/java/org/influxdb/impl/InfluxDBResultMapper.java alla riga 160 e traccia il modo in cui vengono istanziati i measurement objects. Verifica il comportamento con una classe @Measurement package-private e valuta un test di regressione che dimostri che il mapping ha esito positivo per questo livello di visibilità.

Scritto dal modello di indicizzazione a partire dal testo della issue.