Allow generating ESM output from npm (non-breaking)

[aldenquimby]

What did you implement:

Closes #1493

How did you implement it:

• non-breaking alternative approach to Allow generating ESM output from npm #1494
• see this thread to understand why that was a breaking change

How can we verify it:

• my project works when I include this change locally
• generating .js file allows serverless invoke local to work, and including type: module allows the deployed Lambda to work:

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[aldenquimby]

@vicary @j0k3r what are your thoughts on this PR? Anything I can do to help move it forward?

And apologies if tagging you is not the appropriate next step. I'd be happy to start a CONTRIBUTING.md if you let me know the expected process

[vicary]

I am more inclined towards #1494 because it's a smaller change, we can discuss more in details there.

[aldenquimby]

@vicary I closed the other PR and expanded on the README here. Please let me know if there's anything else you'd like to see, thank you!

[vicary]

@aldenquimby Just a few touch ups.

Let's also give it some time for @j0k3r to comment, please also note that we may have some stuck tests that requires resolution from the repo owner before our next release.

[aldenquimby]

Thank you for the help on this @vicary !

[jfroelich]

We're very interested in this PR being merged because the lack of support for ESM is a blocker for us on several projects. Any chances of that happening soon?

[j0k3r]

This looks good to me, can you just squash all commits?