Add missing Smithy dependencies

[trstephen-amazon]

Resubmission of #651 while we debug creds retrieval.

Description of changes: Added explicit dependencies to @smithy/smithy-client and @smithy/node-http-handler, as they were not declared, which causes phantom dependency issues in non-hoisting package managers such as pnpm (with hoisting disabled, as used by Bazel, for example). I've chosen the same version qualifier/selector that is used in transitive dependencies to avoid any unexpected package version variations. This should not affect any of this package's consumers.

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