CI: Docker build image is >400 mb

[kushthedude]

Description

Docker builds image is whooping 400mb.
Expected Behavior

Reduce the docker image size by at least 8 times.

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[leecalcote]

@pranav-bhatt will you confirm whether this issue remains?

[AugustasV]

One way to make image thinner is to use [distroless image] for istio (https://hub.docker.com/layers/proxyv2/istio/proxyv2/1.5.0-distroless/images/sha256-29292a1689e8ee5bec7efb6437b012b5dc8d04cea6da6059088a96ff1da7373f?context=explore)
Most significant size reduce would be to change go image into alpine version https://hub.docker.com/layers/golang/library/golang/1.13.5-alpine3.11/images/sha256-53dd41aad34f015cd945e924847ce5f7ce6f5114ecf5c284a2b7242b9464f046?context=explore