Solution:
Harness Proxy details has to be implicitly set as build args for Docker Build Plugin.
Current Issue:
Harness Proxy needs to be explicitly set as step output variables so that they can be set as build args for Docker Build Plugin
export HTTPS_PROXY="$HARNESS_HTTPS_PROXY"
export HTTP_PROXY="$HARNESS_HTTP_PROXY"
export NO_PROXY="$HARNESS_NO_PROXY"
This is a redundant repeatative obvious step which as an User, I do not need to add a step explicitily.
Business Value:
Users of the Docker Build Plugin step will have better experience and will add intelligence to the step