Always write required query param keys, even if value is unset or empty (#1973)

* fix: issues when sending multipart-upload-related operations with no upload ID by making upload ID required
add: Mandatory trait
add: S3 customization to make Upload Ids mandatory

* add: CHANGELOG.next.toml entry

* update: strategy for tagging shapes as mandatory

* remove: Mandatory trait
undo: S3Decorator changes
add: codegen to generate "else" branch after required query string serialization `if let Some` check
add: missing tokio feature to `TokioTest`

* update: mandatory-query-param.rs tests

* format: run cargo fmt

* update: return BuildError for missing required query params
update: required-query-params.rs tests

* formatting: make RustWriter.paramList more readable
fix: code broken by merge from `main`

* fix: handling of enum strings

* add: codegen tests for required query params
update: required enum query param codegen
add: smithy-rs CHANGELOG.next.toml entry

* fix: presigning.rs test

* fix: use `toType` instead of `asType`
fix: indentation in test