Add supporting for custom Enum in FluxResultMapper in `toPOJO` method

Using enum as a name of tags is a very often case, mapping POJO to InfluxDb works perfectly, but in reverse case it doesn't

I did not check, but it looks as working code (need to check):
```
...
if (fieldType.isEnum()) {
		field.set(object, Enum.valueOf((Class<Enum>) fieldType, value));
                return;
}
...
```