Add `handlerWrapper` configuration option to AWS Lambda instrumentation

[msonnb]

Is your feature request related to a problem? Please describe

Currently, the AWS Lambda instrumentation provides requestHook and responseHook options for customizing span attributes and handling request/response lifecycle events. However, there's no way to wrap the entire patched handler.

At Sentry, we provide a custom wrapHandler function that

• converts callback-based handlers to promise-based ones
• inspects the return value of the handler
• sets a timeout to warn when a handler is near it's max. execution time limit
• and more...

Ideally we'd want to leverage OpenTelemetry's existing auto-wrapping setup, which is why the following API would be very useful:

Describe the solution you'd like to see

Add a handlerWrapper (name open to bikeshedding) option to AwsLambdaInstrumentationConfig:

export type HandlerWrapper = <T extends Handler>(handler: T) => T;

export interface AwsLambdaInstrumentationConfig extends InstrumentationConfig {
  requestHook?: RequestHook;
  responseHook?: ResponseHook;
  eventContextExtractor?: EventContextExtractor;
  lambdaHandler?: string;
  lambdaStartTime?: number;
  // New option
  handlerWrapper?: HandlerWrapper;
}

The implementation would modify the _getHandler method to apply the wrapper after creating the patched handler:

private _getHandler<T extends Handler>(handlerLoadStartTime: number) {
  return (original: T): T => {
    const patchedHandler = this._getPatchHandler(original, handlerLoadStartTime);
    const { handlerWrapper } = this.getConfig();

    if (handlerWrapper) {
      return handlerWrapper(patchedHandler) as T;
    }

    return patchedHandler as T;
  };
}

Describe alternatives you've considered

We currently maintain a vendored version of the AWS Lambda instrumentation that adds Sentry's wrapHandler directly around patchedHandler and thought that this feature might be useful to others as well.

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