Fix documentation links in `aws-smithy-http-server`

[hlbarber]

The links to dependencies in aws-smithy-http-server are broken in docs.rs.

Shorthand links seems to work in some areas (HeaderMap) but not others (tower::Layer).

Investigate why, fix this, and ensure that CI detects it in the future.

[SamantaTarun]

Could you please clarify this issue in more detailed?

[hlbarber]

Could you please clarify this issue in more detailed?

Somewhere between smithy-rs 0.49 and 0.50 some of the documentation links stopped being generated correctly. You can see this change here to here. The issue asks why did this happen? How can we fix it? How can we prevent it happening again?