Make region optional for S3 instructions

[malhotrashivam]

Before this change, region was a mandatory parameter for reading parquet files from S3.
After this change, if region is not provided, it will be picked up by the AWS sdk using the following provider chain:

1. Check the 'aws.region' system property for the region.
2. Check the 'AWS_REGION' environment variable for the region.
3. Check the {user.home}/.aws/credentials and {user.home}/.aws/config files for the region.
4. If running in EC2, check the EC2 metadata service for the region.

Throw exception if not found in any of the locations above

Reference: https://sdk.amazonaws.com/java/api/2.0.0-preview-11/software/amazon/awssdk/awscore/client/builder/AwsClientBuilder.html

Also, since region was the only mandatory parameter in S3 instructions, after this change, reading from S3 will be allowed without passing any S3 instructions. For example, code like the following python example will work, as long as the region, access key and secret key are set properly using properties or config files:

from deephaven import parquet

test = parquet.read("s3://bucket-name/file-name.parquet")   # Note no s3 instructions

[rcaudy]

My comments are the same as Larry's.

[rcaudy]

Caught up

[jmao-denver]

Python changes LGTM

[deephaven-internal]

Labels indicate documentation is required. Issues for documentation have been opened:

Community: deephaven/deephaven-docs-community#234