docker: Libervia revision can now be specified: Using the `DOCKER_LIBERVIA_REV` environment variable, backend (and related repos) revision can now be specified. By default (variable empty or not set), the current `tip` version is used, and `dev` is used for tagging. If the variable is set, the revision will be used and used for tagging the image.

ARG REVISION=dev
FROM libervia/web:${REVISION}

LABEL maintainer="Goffi <tmp_dockerfiles@goffi.org>"

ARG DEBIAN_FRONTEND=noninteractive

USER root

COPY --chown=root:root libervia.conf /etc/libervia.conf

WORKDIR /home/libervia
USER libervia