Improve the creation of ExecutorService when reading footers

Doing some benchmarks loading a large set of parquet files (3000+) from the local FS, we observed some inefficiencies in the number of created threads when reading footers.

By reading, the read the configuration parallelism in Hadoop configuration (defaulted to 5) and allocate 2 ExecuteService with each 5 threads to read footers. This is especially inefficient if there is less Callable to handle than the configured parallelism.

**Reporter**: [Benoit Lacelle](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=blasd)

_{**Note**: *This issue was originally created as [PARQUET-1055](https://issues.apache.org/jira/browse/PARQUET-1055). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

El issue identifica la lectura de footers y el paralelismo de la configuración de Hadoop como puntos de entrada. Rastrea dónde se crean las dos instancias de ExecutorService y compara su tamaño con el número de tareas Callable de footer. Se considera terminado cuando se evitan hilos excesivos si hay menos tareas que el paralelismo configurado.

Escrito por el modelo de indexación a partir del texto del issue.