Update parsing of headers to be infallible (by parsing failed UTF-8 headers as ISO-8859)

[landonxjames]

Motivation and Context

Some users have encountered an issue with where the SDK fails when parsing the content-disposition header from S3's GetObject because the header contain bytes for ISO-8859 encoded strings rather than the UTF-8 we were expecting. This is difficult to handle because the SDK has been designed to assume that all headers are UTF-8 and so they are all represented as Rust String types that only support UTF-8.

This PR implements fallback parsing where bytes that fail to parse as UTF-8 are instead parsed as ISO-8859 in an infallible way.

This is just meant as a jumping off point for discussions of how to handle this problem and should NOT BE MERGED without a group consensus.

Description

Update the TryFrom impls for HeaderMap from http_1x and http_02x to fallback to parsing headers as ISO-8859 when UTF-8 parsing fails. This is done by replacing bytes that are outside the 0-127 ASCII range with a two byte UTF-8 codepoint.

Testing

Added new tests confirming that ISO-8859 headers are correctly parsed to UTF-8.

Checklist

• For changes to the smithy-rs codegen or runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "client," "server," or both in the applies_to key.
• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

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[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.