Feature: add TimeoutError variant to SdkError (#886)

* feature: add TimeoutError variant to SdkError
add: TimeoutError variant to ImdsError
update: tests broken by new variant

* update: changelogs

* add: new inner timeout error RequestTimeoutError
update: tests broken by new inner error
rename: aws_smithy_client::hyper_ext::TimeoutError to HttpTimeoutError
add: missing dep to integration test

* revert: IMDS error change
update: content for HttpTimeoutError
fix: clippy lint

* add: back the source method to HttpTimeoutError
update: connector timeout tests
remove: TODO