Use arrow object_store instead of aws_sdk_s3

[trueleo]

Fixes #70 .

Description

• Replace aws_sdk_s3 client with object_store::aws client

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.