CODEOWNERS: some runtime crates are shared ownership (#1889)

These crates are used by server SDKs too. `CODEOWNERS` currently says
they are exclusively owned by the AWS Rust SDK team.

See #1887 (comment).

CODEOWNERS

@@ -17,3 +17,14 @@
 /design/                                        @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
 /gradle.properties                              @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
 /tools/                                         @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-async/                 @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-eventstream/           @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-http/                  @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-json/                  @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-protocol-test/         @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-types/                 @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-types-convert/         @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/aws-smithy-xml/                   @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/inlineable/                       @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/build.gradle.kts                  @awslabs/rust-sdk-owners @awslabs/smithy-rs-server
+/rust-runtime/Cargo.toml                        @awslabs/rust-sdk-owners @awslabs/smithy-rs-server