fix(aws-cdk): configure zip directory to follow symlinks

[justinmchase]

When building a nodejs lambda it is really common for dependencies under the node_modules folder to actually be symlink'd to other folders on your system. Currently, when creating a lambda with a dependencies linked this way, it will package the symlink itself and not the files within it.

For example, if you create a lambda function like this:

const example = new Function(this, 'Example'), {
  runtime: Runtime.NodeJS810,
  handler: "index.handler",
  code: Code.directory("example"))
});

And if that example code directory has a dependency like this in its package.json:

"dependencies": {
  "helpers": "../helpers"
}

When calling npm i before deployment, it will actually generate a symlink to the helpers directory node_modules/helpers -> ../helpers. Trying to deploy such a lambda function results in an error when you execute the lambda since the files within the symlink'd folder were not included in the zip and therefore were not deployed up to lambda.

This change simply configures the archiver to follow symlinks when building the zip file. It is not a breaking change as all existing directory structures should work, there is no scenario where a previously working zipdirectory would now not be working. None that I know of at least.

Fixes #731

---

Testing

• Unit test and/or integration test added
• Toolkit change?: N\A
• Init template change?: N\A

Documentation

• README: README and/or documentation topic updated
• jsdocs: All public APIs documented

Title and description

• Change type: Title is prefixed with change type:
  • fix(module): <title> bug fix (patch)
  • feat(module): <title> feature/capability (minor)
  • chore(module): <title> won't appear in changelog
  • build(module): <title> won't appear in changelog
• Title format: Title uses lower case and doesn't end with a period
• Breaking change?: Last paragraph of description is: BREAKING CHANGE: <describe exactly what changed and how to achieve similar behavior + link to documentation/gist/issue if more details are required>
• References: Indicate issues fixed via: Fixes #xxx or Closes #xxx

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[rix0rrr]

I'm slightly concerned about in-archive symlinks (wasted space) and recursive symlinks (infinite recursion?)

I feel we could optimize those some more. But at the same time, I will concede it's probably not a big concern.

[eladb]

How hard it is to preserve symlinks for links inside the same directory? Does the glob library support something like this?

[justinmchase]

@rix0rrr glob will prevent infinite reference loops:
isaacs/node-glob#252

@eladb I believe if you link to the same folder twice it will copy the files into the zip twice. I don't think its supported in glob to have a partial solution, preserve symlinks that are subdirs and follow those that are not... but it seems like that would actually be doable from looking in glob. It would require adding the feature to glob I think but it would probably be a medium-low complexity feature I would guess.