NativeDatasetFactory parameter allocator and memory pool relationship

### Describe the usage question you have. Please include as many useful details as possible.

@zhztheplayer
```
/**
* Constructor.
*
* @param allocator a context allocator associated with this factory. Any buffer that will be created natively will
* be then bound to this allocator.
* @param memoryPool the native memory pool associated with this factory. Any buffer created natively should request
* for memory spaces from this memory pool. This is a mapped instance of c++ arrow::MemoryPool.
* @param datasetFactoryId an ID, at the same time the native pointer of the underlying native instance of this
* factory. Make sure in c++ side the pointer is pointing to the shared pointer wrapping
* the actual instance so we could successfully decrease the reference count once
* {@link #close} is called.
* @see #close()
*/
public NativeDatasetFactory(BufferAllocator allocator, NativeMemoryPool memoryPool, long datasetFactoryId) {
this.allocator = allocator;
this.memoryPool = memoryPool;
this.datasetFactoryId = datasetFactoryId;
}
```

what's the relationship between allocator and memoryPool, does allocator allocate buffers from the memory pool or there is no such restrictions?

thanks

### Component(s)

Java

Comienza con el constructor de NativeDatasetFactory mostrado en el issue y sigue cómo se usan BufferAllocator y NativeMemoryPool. Aclara su relación en la documentación de la API de Java, incluido lo que los contributors pueden verificar a partir de la ruta de asignación nativa; se considera completado cuando la pregunta sobre el uso queda respondida claramente.

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