Docker: Install NodeJS and Yarn in Ubuntu 18.04

You will need BOTH yarn and nodejs from external resources because the Ubuntu repo versions are very old.

RUN apt install curl gnupg2 -y
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN curl -sL https://deb.nodesource.com/setup_14.x | bash -
RUN apt update -y
RUN apt install nodejs yarn -y