Docker options for running Docker Lambda within a Docker container

[apancutt]

Description

Extends PR #961 with additional changes:

• Merge conflicts resolved
• Restored pull of latest Docker Lambda image upon start
• Added dockerNetwork option
• Enabled DOCKER_LAMBDA_WATCH to restart Docker Lambda on filesystem changes
• Documented new options in README.md
• Removed trailing whitespace in README.md
• Sorted command options in README.md
• Sorted properties in defaultOptions.js
• Fixed code style violation in DockerContainer.js as required by prettier

Motivation and Context

Cold starts with vanilla serverless-offline are extremely slow (we were getting average response times of ~700ms with a Koa API). The useDocker option addresses this by keeping a container warm but this has several issues...

1. it doesn't work when running serverless-offline within a Docker container; typical of complex development stacks using Docker Compose (fixed by --dockerHost and --dockerHostServicePath options)
2. it doesn't hot-reload when files change (fixed by adding DOCKER_LAMBDA_WATCH=1 to Docker container env)
3. the container cannot communicate with other containers hosted on the parent Docker Compose stack (fixed by --dockerNetwork option).

How Has This Been Tested?

Tested within a development environment provisioned using Docker Compose running several service containers, one of which is serverless-offline. The API running in this container is now fully operational with the --useDocker option enabled and hot-reloads on file changes. Response times reduced from ~700ms to ~60ms.

[frozenbonito]

Thank you for your great work @apancutt.
Sorry, There are still some issues about artifact and layer support.
Let me fix them and add test.

[frozenbonito]

@apancutt
Could you enable Allow edits from maintainers ?
https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/allowing-changes-to-a-pull-request-branch-created-from-a-fork

[apancutt]

That's already enabled. Not working?

[frozenbonito]

For some reason, I couldn't push to your repository directly.
Could you merge the following branch to this PR?
https://github.com/frozenbonito/serverless-offline/tree/pull/1164

[frozenbonito]

Thank you!