`aws_smithy_http_server::*` should be re-exported from generated crates (#3839)

Many customers have reported the need to explicitly depend on the
`aws-smithy-http-server` crate in their service handler code. When they
re-generate the crate, they often encounter version mismatches between
the `aws-smithy-http-server` crate used in the generated code and the
one they use in their service handler. This version discrepancy leads to
compilation errors, requiring them to manually adjust the crate
versions, which adds friction to their development workflow.

To resolve this issue, we now re-export all relevant types from
`aws-smithy-http-server` within the generated crates. By doing so,
customers can use these re-exported types directly, eliminating the need
to depend on `aws-smithy-http-server` in their handler code.

Additionally, the generated crates no longer have the `aws-lambda`
feature flag enabled by default. This prevents the `aws-lambda` feature
from being automatically enabled in `aws-smithy-http-server` when the
SDK is not intended for AWS Lambda.

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Co-authored-by: Fahad Zubair <fahadzub@amazon.com>