Support docker build comparable --ssh switch about kaniko HOT 1 OPEN

FROM golang:alpine
RUN apk update && apk add --no-cache git && apk add openssh

# Private repo
ARG PRIVATE_SCM_HOST
ARG PRIVATE_SCM_SSH_PORT

ENV GOPRIVATE=$PRIVATE_SCM_HOST

# SSH Key setup
RUN mkdir -p /root/.ssh && \
    chmod 0700 /root/.ssh && \
    ssh-keyscan -p $PRIVATE_SCM_SSH_PORT -H $PRIVATE_SCM_HOST > /root/.ssh/known_hosts

# Configure https to ssh mapping
RUN git config --global url."ssh://git@$PRIVATE_SCM_HOST:$PRIVATE_SCM_SSH_PORT".insteadOf "https://$PRIVATE_SCM_HOST/scm"

# Create app directory
WORKDIR /opt/apiserver

# Bring source into the container and build
COPY . .
RUN --mount=type=ssh go mod download
RUN --mount=type=ssh go build -o /opt/apiserver/apiserver -buildvcs=false

CMD [ "/opt/apiserver/apiserver" ]

docker build --build-arg PRIVATE_SCM_HOST=github.com/username/repo --build-arg PRIVATE_SCM_SSH_PORT=22 --build-arg --ssh default .