[v2] S3 expires timestamp port

[aemous]

Issue #, if available:

Description of changes:
Ported boto/botocore#3232 from botocore, which gracefully handles invalid expires timestamps from S3.

Testing:
In addition to passing existing and newly added tests for this functionality, I did manual testing to verify the new field is included in the response body of the GetObject operation. Below is an example manual test using the command aws s3api get-object --bucket bucketname --key filename outfile:

}
    "AcceptRanges": "bytes",
    "LastModified": "2024-09-20T18:56:59+00:00",
    "ContentLength": 23230,
    "ETag": "\"207d91b3fd7953aac7b28b8ddf882953\"",
    "ContentType": "binary/octet-stream",
    "Expires": "2025-09-20T07:28:00+00:00",
    "ServerSideEncryption": "AES256",
    "Metadata": {},
    "ExpiresString": "Sat, 20 Sep 2025 07:28:00 GMT"
}

This can be compared to the output of the exact same command using the current latest release:

{
    "AcceptRanges": "bytes",
    "LastModified": "2024-09-20T18:56:59+00:00",
    "ContentLength": 23230,
    "ETag": "\"207d91b3fd7953aac7b28b8ddf882953\"",
    "ContentType": "binary/octet-stream",
    "Expires": "2025-09-20T07:28:00+00:00",
    "ServerSideEncryption": "AES256",
    "Metadata": {}
}

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