fix: move smithy config customization into the smithy code generator (#1599)

* fix: move smithy config customization into the smithy code generator

* add: CHANGELOG entry

* update: tests

* fix: config codegen tests

* update: hide config fields and provide accessors instead

* fix: usage of private fields
add: accessor docs

* format: run ktlint

* fix: update more old code

* update: clone sleep_impl since that's why people access it

* update: CHANGELOG.next.toml

* Update CHANGELOG.next.toml

Co-authored-by: John DiSanti <jdisanti@amazon.com>

Co-authored-by: John DiSanti <jdisanti@amazon.com>