Add missing setters to ConfigLoader (#4027)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
Customer reported that the `request_checksum_calculation` and
`response_checksum_validation` setters were missing from the
`ConfigLoader`, but were present on the `SdkConfig` builder. This PR
adds those setters.

## Description
<!--- Describe your changes in detail -->

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] For changes to the AWS SDK, generated SDK code, or SDK runtime
crates, I have created a changelog entry Markdown file in the
`.changelog` directory, specifying "aws-sdk-rust" in the `applies_to`
key.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

Author: landonxjames

.changelog/config_loader_setters.md

@@ -0,0 +1,10 @@
+---
+applies_to: ["aws-sdk-rust"]
+authors: ["landonxjames"]
+references: ["smithy-rs#920"]
+breaking: false
+new_feature: false
+bug_fix: true
+---
+
+Add missing `request_checksum_calculation` and `response_checksum_validation` setters to the `ConfigLoader`

aws/rust-runtime/aws-config/Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "aws-config"
-version = "1.5.17"
+version = "1.5.18"
 authors = [
     "AWS Rust SDK Team <aws-sdk-rust@amazon.com>",
     "Russell Cohen <rcoh@amazon.com>",

aws/rust-runtime/aws-config/Cargo.toml

@@ -732,6 +732,36 @@ mod loader {
             self
         }
 
+        /// Set the checksum calculation strategy to use when making requests.
+        /// # Examples
+        /// ```
+        /// use aws_types::SdkConfig;
+        /// use aws_smithy_types::checksum_config::RequestChecksumCalculation;
+        /// let config = SdkConfig::builder().request_checksum_calculation(RequestChecksumCalculation::WhenSupported).build();
+        /// ```
+        pub fn request_checksum_calculation(
+            mut self,
+            request_checksum_calculation: RequestChecksumCalculation,
+        ) -> Self {
+            self.request_checksum_calculation = Some(request_checksum_calculation);
+            self
+        }
+
+        /// Set the checksum calculation strategy to use for responses.
+        /// # Examples
+        /// ```
+        /// use aws_types::SdkConfig;
+        /// use aws_smithy_types::checksum_config::ResponseChecksumValidation;
+        /// let config = SdkConfig::builder().response_checksum_validation(ResponseChecksumValidation::WhenSupported).build();
+        /// ```
+        pub fn response_checksum_validation(
+            mut self,
+            response_checksum_validation: ResponseChecksumValidation,
+        ) -> Self {
+            self.response_checksum_validation = Some(response_checksum_validation);
+            self
+        }
+
         /// Load the default configuration chain
         ///
         /// If fields have been overridden during builder construction, the override values will be used.
@@ -980,6 +1010,7 @@ mod loader {
         use aws_types::app_name::AppName;
         use aws_types::origin::Origin;
         use aws_types::os_shim_internal::{Env, Fs};
+        use aws_types::sdk_config::{RequestChecksumCalculation, ResponseChecksumValidation};
         use std::sync::atomic::{AtomicUsize, Ordering};
         use std::sync::Arc;
 
@@ -1160,6 +1191,30 @@ mod loader {
             assert_eq!(Some(&app_name), conf.app_name());
         }
 
+        #[tokio::test]
+        async fn request_checksum_calculation() {
+            let conf = base_conf()
+                .request_checksum_calculation(RequestChecksumCalculation::WhenRequired)
+                .load()
+                .await;
+            assert_eq!(
+                Some(RequestChecksumCalculation::WhenRequired),
+                conf.request_checksum_calculation()
+            );
+        }
+
+        #[tokio::test]
+        async fn response_checksum_validation() {
+            let conf = base_conf()
+                .response_checksum_validation(ResponseChecksumValidation::WhenRequired)
+                .load()
+                .await;
+            assert_eq!(
+                Some(ResponseChecksumValidation::WhenRequired),
+                conf.response_checksum_validation()
+            );
+        }
+
         #[cfg(feature = "rustls")]
         #[tokio::test]
         async fn disable_default_credentials() {