fix(backend/s3): properly parse boolean environment variables for FIPS and DualStack endpoints

[gautamrajur]

Description

The boolAttrDefaultEnvVarOk function was incorrectly treating any non-empty environment variable value as true. This caused AWS_USE_FIPS_ENDPOINT=false and AWS_USE_DUALSTACK_ENDPOINT=false to incorrectly enable these endpoints instead of disabling them.

The fix uses strconv.ParseBool to properly parse boolean values from environment variables, accepting standard boolean representations:

• true: "1", "t", "T", "TRUE", "true", "True"
• false: "0", "f", "F", "FALSE", "false", "False"

Invalid boolean values in environment variables are now ignored, falling back to the default behavior.

Fixes #37601

Target Release

1.15.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

No changes to security controls.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.

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[crw]

This appears to be a duplicate of #37940 -- can this be closed while we focus on the preceding PR?

[jar-b]

Hello @gautamrajur - thank you for taking the time to open this. The primary difference between this and #37940 is that "truthy" values (t, 1, f, 0) are supported in addition to true and false. While more flexible, this diverges from the behavior of the AWS SDK for Go (see here and here).

With this in mind we will be closing this out in favor of #37940.

[github-actions]

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