docs: add --skip-auth flag documentation

[anasstahr]

Summary

Changes

• Add --skip-auth to the configuration parameters table in README
• Add an "Unsigned requests" section under Troubleshooting explaining how to connect to endpoints that don't require SigV4 credentials

User experience

Users can now find documentation for the --skip-auth flag directly in the README, including when and how to use it for endpoints that don't require AWS IAM authentication.

Checklist

• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Is this a breaking change? (Y/N)

• Yes
• No

Please add details about how this change was tested.

• Did integration tests succeed?
• If the feature is a new use case, is it necessary to add a new integration test case?

Acknowledgment

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