Support parquet load for Neptune Analytics

[theneelshah]

Issue #751:

Description of changes:

• Add support for parquet format for incremental data load in AWS Neptune Analytics.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[adityaramesh12]

Modified the description message.
Can you verify/validate if incremental load with neptune database is possible as well? I think there is a condition that switches between incremental load and bulk load for neptune analytics v/s neptune. The code changes should be sufficient. But let's double check and document it here.
If that is not the case, we would need to add an explicit condition to only permit parquet load for Neptune Analytics.