Support local errors with NPM 7 workspaces

[mikejpeters]

What did you implement:

Closes #781

How did you implement it:

When parsing npm ls stderr, ignore npm ERR! code ELSPROBLEMS and then all lines after the opening { (start of JSON and error summary).

How can we verify it:

I added a new test.

It should also resolve the issue demonstrated at this minimum example repo: boundstate/serverless-webpack-npm-7-example

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

[j0k3r]

Looks ok to me 👍

[j0k3r]

Could you rebase against the master? Thanks

[mikejpeters]

Done