Allow to keep the output directory

[jaydp17]

What did you implement:

Closes #453
Closes #467

How did you implement it:

There's an option we can pass keepOutputDirectory, which will skip the cleanup process.

# serverless.yml
custom:
  webpack:
    keepOutputDirectory: true

How can we verify it:

1. As described above, just add the flag in serverless.yml.
2. Run sls package
3. Verify that .webpack is present

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

[abbottry]

This would be extremely helpful. I'm unsure why this plugin takes this action -- it prevents serverless-s3-sync from working properly as when it attempts to sync, the directory is gone.

[colkito]

any scheduled date for merge this PR?

[jaydp17]

@colcodev, I'm not sure about it.
May be @HyperBrain is super busy, but then again it's been over 3 months since the PR opened.
Anyways, I have been using the fork, so if you need this immediately, that could be one of the options.

[HyperBrain]

@jaydp17 I indeed was super busy the last few months. Sorry for that. The feature looks ok to me and should be part of 5.3.0 as it is a new feature.

[HyperBrain]

LGTM 👍