lambda-js: Add note about esbuild module exports

This change adds a short blurb about requirements for users who are using esbuild.

As discussed in aws-observability/aws-otel-lambda#99 there is a quirk of esbuild that causes exported functions using the `export` keyword to be marked immutable in the transpiled JS. As a result, you must use `module.exports` instead, which is passed along by the esbuild transpilation process unscathed.

src/docs/getting-started/lambda/lambda-js.mdx

@@ -19,6 +19,8 @@ The AWS managed Lambda layer for ADOT JavaScript provides a plug and play user e
 
 The Lambda layer supports Node.JS v14+ Lambda runtimes. For more information about supported JavaScript and Node.JS versions, see the [OpenTelemetry JavaScript documentation](https://github.com/open-telemetry/opentelemetry-js).
 
+For *TypeScript users*, if you are using `esbuild` (either directly or through tools such as the AWS CDK), you *must* export your handler function through `module.exports` rather than with the `export` keyword! The AWS mananaged layer for ADOT JavaScript needs to hot-patch your handler at runtime, but can't because `esbuild` makes your handler immutable when using the `export` keyword. 
+
 ### Add the ARN of the Lambda Layer
 
 In this section, we consume the Lambda layer for use with Node.JS Lambda Functions. This includes a reduced version of the [AWS Distro for OpenTelemetry Collector (ADOT Collector)](https://github.com/aws-observability/aws-otel-collector), which runs as a Lambda extension.