Ubuntu with default user who can use sudo unless password.

Dockerfile

FROM ubuntu

ARG USERNAME=user
ARG USERPASS=user
ARG GROUPNAME=user
ARG UID=1000
ARG GID=1000

RUN apt -y update && apt install -y sudo

RUN groupadd -g $GID $GROUPNAME && \
    useradd -m -s /bin/bash -p $USERPASS -u $UID -g $GID $USERNAME && \
    gpasswd -a $USERNAME sudo && \
    echo "$USERNAME:$USERPASS" | chpasswd && \
    echo "user ALL=NOPASSWD: ALL" >> /etc/sudoers
USER $USERNAME

WORKDIR /home/$USERNAME/