Bump `lambda_http` dependency of `aws-smithy-http-server` to 0.8.0 (#2685) (#2691)

This is https://github.com/awslabs/smithy-rs/pull/2685 again, which was
merged
prematurely and reverted in
https://github.com/awslabs/smithy-rs/pull/2690.

This time we won't merge it until it's due time.

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