fix(aws-sdk): use custom client_context prop

In every other language the respected property is `custom`
e.g.
- https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/9a7f7125ab3f77c47a46be524f29e150536fba6f/instrumentation/aws-sdk/aws-sdk-2.2/library/src/main/java/io/opentelemetry/instrumentation/awssdk/v2_2/internal/LambdaImpl.java#L41

Author: smoke

plugins/node/opentelemetry-instrumentation-aws-sdk/doc/lambda.md

@@ -9,4 +9,4 @@ The following methods are automatically enhanced:
 ### Invoke
 
 - Attributes are added by this instrumentation according to the [spec for Outgoing Invocations of a FaaS from a client](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/faas.md#outgoing-invocations) .
-- OpenTelemetry trace context is injected into the `ClientContext` parameter, allowing functions to extract this using the `Custom` property within the function.
+- OpenTelemetry trace context is injected into the `ClientContext` parameter, allowing functions to extract this using the `custom` property within the function.

plugins/node/opentelemetry-instrumentation-aws-sdk/src/services/lambda.ts

@@ -109,8 +109,8 @@ const injectLambdaPropagationContext = (
 
     const updatedClientContext = {
       ...parsedClientContext,
-      Custom: {
-        ...parsedClientContext.Custom,
+      custom: {
+        ...parsedClientContext.custom,
         ...propagatedContext,
       },
     };

plugins/node/opentelemetry-instrumentation-aws-sdk/test/lambda.test.ts

@@ -148,7 +148,7 @@ describe('Lambda', () => {
             'base64'
           ).toString()
         ) as Record<string, any>;
-        expect(clientContext.Custom).toHaveProperty('traceparent');
+        expect(clientContext.custom).toHaveProperty('traceparent');
       });
 
       it('should skip context propagation in the event it would push the ClientContext over 3583 bytes', async () => {
@@ -168,7 +168,7 @@ describe('Lambda', () => {
 
         const existingClientContext = Buffer.from(
           JSON.stringify({
-            Custom: {
+            custom: {
               text: [...Array(2600)]
                 .map(x => String.fromCharCode(48 + Math.random() * 74))
                 .join(''),
@@ -221,7 +221,7 @@ describe('Lambda', () => {
           ),
           ClientContext: Buffer.from(
             JSON.stringify({
-              Custom: {
+              custom: {
                 existing: 'data',
               },
             })
@@ -238,8 +238,8 @@ describe('Lambda', () => {
             'base64'
           ).toString()
         ) as Record<string, any>;
-        expect(clientContext.Custom).toHaveProperty('existing', 'data');
-        expect(clientContext.Custom).toHaveProperty('traceparent');
+        expect(clientContext.custom).toHaveProperty('existing', 'data');
+        expect(clientContext.custom).toHaveProperty('traceparent');
       });
 
       it('should maintain any existing top-level fields in the client context', async () => {
@@ -265,7 +265,7 @@ describe('Lambda', () => {
             platform: 'Symbian',
             platformVersion: '9.2',
           },
-          Custom: {
+          custom: {
             existing: 'data',
           },
         };
@@ -293,7 +293,7 @@ describe('Lambda', () => {
           ).toString()
         ) as Record<string, any>;
         expect(updatedClientContext.env).toStrictEqual(clientContext.env);
-        expect(updatedClientContext.Custom).toHaveProperty('traceparent');
+        expect(updatedClientContext.custom).toHaveProperty('traceparent');
       });
 
       // It probably should be valid JSON, and I'm not sure what the lambda internals make of it if