Skip empty configuration values when writing AWS CLI config

[Gopesh111]

Issue #, if available:
N/A

Description of changes:
This change prevents empty or whitespace-only configuration values from being
written to AWS CLI config files.

Previously, passing an empty value could result in invalid or confusing
configuration entries (e.g., region =), which may cause unexpected behavior
later. This update skips writing such values while preserving existing behavior
for valid inputs.

A unit test is included to cover this edge case.

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redistribute this contribution, under the terms of your choice.

[Gopesh111]

Hi team, I just wanted to follow up on this PR to see if there’s anything else needed from my side. I’ve included unit tests to ensure empty configuration values are skipped as described. Happy to make any adjustments based on your feedback!

[Gopesh111]

Hi @aws-cli-maintainers,

I'm following up on this PR to see if it can be scheduled for review. This change addresses a small but important edge case where empty or whitespace-only values are written to the AWS CLI config, potentially causing issues with downstream commands.

I have already included unit tests covering this behavior. Please let me know if there are any specific AWS contribution guidelines or further tests you'd like me to implement to move this forward.

Thank you!