Implemented an optimized dockerfile for better build time and dev-container size

[kmehant]

Explanation to changes implemented

• Shifted the base image to python:3-slim from python:3. Reason: This is done to reduce the size of the docker image and to optimize the initial docker image build time by Visual Studio Code.

• Ran multiple consecutive RUN commands in a single intermediate container Reason: In order to further optimize Dockerfile by reducing the number of Docker layers and for faster builds and lighter containers.

• Removed the below layer as WORKDIR does that job for us.

  RUN mkdir /workspace

Results:

• Faster docker builds by Visual Studio Code
• Lighter docker dev-container
• docker image size reduced to ~330 MB

  Issue

  Fixes #4

Tested locally through vs code

[msftclas]

All CLA requirements met.

[kmehant]

@Chuxel @egamma I would like to receive a review upon my work :)

[egamma]

@kmehant what was the reason for closing the PR?

[kmehant]

Hi @egamma thanks a lot for looking in to this. I had spoken to Chuck about this. I agree with the points that

• Slim version must be tested beyond the docs to replace the normal base image version
• Other changes which I made might not contribute to large optimizations and I think seem to collide with the usual template being used for all the examples. @egamma I wish you would look at this issue https://github.com/microsoft/vscode-dev-containers/issues/66 And other PRs I have made to https://github.com/microsoft/vscode-dev-containers/