container spec for building Penumbra under Ubuntu 20.04

Containerfile

FROM ubuntu:focal as builder
RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
        build-essential \
        clang \
        libssl-dev \
        pkg-config \
        git \
        curl

RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
RUN mkdir /app && git clone https://github.com/penumbra-zone/penumbra /app
WORKDIR /app
ARG GIT_REF=041-callirrhoe
RUN git fetch --tags
RUN git checkout "${GIT_REF}"
RUN . ~/.cargo/env && cargo build --release
FROM ubuntu:focal
COPY --from=builder /app/target/release/pd /app/target/release/pcli /usr/local/bin/