Update MSRV to 1.66.1 (#2468)

* update: MSRV to 1.66.1

* add: CHANGELOG.next.toml entry

* update: Dockerfile too

* fix: clippy lints

* fix: sigv4 event_stream.rs clippy lint
update: codegen clippy lint allowlist

* fix: doc lint that's nightly only
add: docs for aws-smithy-http
add: docs for aws-smithy-client
add: docs for aws-smithy-async

* add: more missing docs.

* fix: add more missing docs

* remove: unnecessary & in HttpBindingGenerator
fix: lint name

* fix: another doc import

* fix: test broken by changing compiler error

* fix: even more lints\nadd: lint warns to all smithy runtime crates

* fix: broken doc links

* fix: clippy bug

* fix: don't use modules named lib in codegen tests

* fix: the paginator_canary.rs unnecessary cast