core: add new `init_script_path` option: `init_script_path` option can be used in `[DEFAULTS]` to run a script at the end of backend initialisation. A new `init_pre_script` method is used to wait for backend to reach this stage (designed to be used mostly by CLI frontend), then the usual `ready_get` method is finished once the script is finished.

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

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