build: use uid of user building the build containers

contrib/build-linux/appimage/Dockerfile

@@ -4,6 +4,8 @@
 
 FROM debian:buster@sha256:233c3bbc892229c82da7231980d50adceba4db56a08c0b7053a4852782703459
 
+ARG UID=1000
+
 ENV LC_ALL=C.UTF-8 LANG=C.UTF-8
 ENV DEBIAN_FRONTEND=noninteractive
 
@@ -75,7 +77,7 @@ ENV USER="user"
 ENV HOME_DIR="/home/${USER}"
 ENV WORK_DIR="${HOME_DIR}/wspace" \
     PATH="${HOME_DIR}/.local/bin:${PATH}"
-RUN useradd --create-home --shell /bin/bash ${USER}
+RUN useradd --uid $UID --create-home --shell /bin/bash ${USER}
 RUN usermod -append --groups sudo ${USER}
 RUN echo "%sudo ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
 WORKDIR ${WORK_DIR}