fix: provide ES module wrapper using conditional exports

[trivikr]

Issue

Attempt to fix: #2754

Description

Add ESModule wrapper using conditional exports, so that import in Node.js will use ES module.

Testing

Linked packages from workspace using the following command:

$ pwd
/home/trivikr/workspace/aws-sdk-js-v3/clients/client-s3

$ npm link                      
...
/local/home/trivikr/.fnm/node-versions/v14.17.4/installation/lib/node_modules/@aws-sdk/client-s3 -> /local/home/trivikr/workspace/aws-sdk-js-v3/clients/client-s3

The error is still thrown when test.mjs is run after running npm link @aws-sdk/client-s3

$ cat test.mjs
import { S3 } from "@aws-sdk/client-s3";

Additional context

API reference: https://nodejs.org/api/packages.html#packages_approach_1_use_an_es_module_wrapper

---

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[trivikr]

Adding "type": "module" doesn't help, as we have to export with .js files.

The test code fails with:

internal/process/esm_loader.js:74
    internalBinding('errors').triggerUncaughtException(
                              ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/local/home/trivikr/workspace/aws-sdk-js-v3/clients/client-s3/dist/es/S3Client' imported from /local/home/trivikr/workspace/aws-sdk-js-v3/clients/client-s3/dist/es/index.js
    at finalizeResolution (internal/modules/esm/resolve.js:285:11)
    at moduleResolve (internal/modules/esm/resolve.js:708:10)
    at Loader.defaultResolve [as _resolve] (internal/modules/esm/resolve.js:819:11)
    at Loader.resolve (internal/modules/esm/loader.js:89:40)
    at Loader.getModuleJob (internal/modules/esm/loader.js:242:28)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:73:40)
    at link (internal/modules/esm/module_job.js:72:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

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