feat(lambda) add docker image support for lambda.

[Schartey]

We are currently restricted to usage of a node sandbox as lambda server.

With this pull request I want to add support for docker containers to run as lambda server. This allows developers to use any server language they want to develop lambdas.

How does it work:

• Rebased the Dockerfile on a dind ubuntu image, so we can start docker images on alpha.
• Added multiple flags to lambda: docker-image, docker-user, docker-password, docker-registry
• If docker-image flag is set, alpha tries to download docker image and runs image as container instead of node

Example:
I have created an example repository that uses golang as lambda server.
Here you can find an example docker-compose file on how to start the alpha server with docker image.

What's missing:

• admin api update
  Allow update of docker image through admin api
• Refactoring
• Tests
• Your opinion

About alternatives:
I thought a lot about alternatives and tried to implement WebAssembly as runtime, but it is still very restricted. I could only make it work with Rust and Typescript, but I think Docker is a better and simpler alternative.

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This change is 

[Schartey]

After some discussions in discuss, I will close this pull request and create a new one for WASM support in lambdas in due time.