Use aws_profile to fetch credentials

[trueleo]

Fixes #372.

Description

Alternate method to fetch credentials on AWS.

AwsBuilder's with_profile builder method name is exposed as a configuration option with env P_S3_PROFILE_NAME. This option conflicts with P_S3_ACCESS_KEY and P_S3_SECRET_KEY

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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.