Allow flexible source-or-PyPI installation via build args

[Geogouz]

While building the images, it would be helpful to developers to introduce logic to optionally get Rucio directly from some repo using a specified Git reference (e.g. master/tag/etc.), instead of always fetching it from PyPI (e.g. because for example some required dependency might have not been released yet by us there).

I suggest this because if a clear section about this option is available in the Dockerfile, it becomes easy for the devs to understand what needs to be adapted for new dependencies to be properly introduced and tested. Otherwise, they will have to spend time in understanding how things need to be configured.

[Geogouz]

To be more specific, my suggestion was to update the Dockerfiles like the server one, from:

ARG TAG
RUN python3 -m pip install --no-cache-dir --pre rucio[oracle,mysql,postgresql]==$TAG

to something like this so that we allow devs to work with new Rucio dependencies that are not yet released:

# ----------------------------------------------------------------------------
# Build‑time parameters
# ----------------------------------------------------------------------------
ARG TAG
ARG RUCIO_REF
ARG RUCIO_REPO="https://github.com/rucio/rucio.git"
ARG RUCIO_EXTRAS="oracle,mysql,postgresql"

# ----------------------------------------------------------------------------
# Upgrade toolchain and install (or build) rucio‑clients
# ----------------------------------------------------------------------------
# • TAG          – The version/release tag to install from PyPI (e.g. 37.0.0).
# • RUCIO_REF    – The Git ref (commit, branch, or tag).
#                  If empty      → install the published wheel from PyPI.
#                  If non‑empty  → build Rucio from that ref and install the resulting wheel.
# • RUCIO_REPO   – The Rucio Git URL to clone when building from source (when RUCIO_REF is set).
#                  It points to the official Rucio repository (but can be changed manually).
# • RUCIO_EXTRAS – The selected Rucio extras to install. \

RUN python3 -m pip install --no-cache-dir --upgrade pip setuptools wheel && \
    if [ -z "$RUCIO_REF" ]; then \
        # ------------------ Install released wheel from PyPI ----------------
        python3 -m pip install --no-cache-dir --pre \
            "rucio[${RUCIO_EXTRAS}]==${TAG}"; \
    else \
        # ---------------- Build wheel from source, then install -------------
        dnf install -y git && \
        python3 -m pip install --no-cache-dir build && \
        git clone "${RUCIO_REPO}" /tmp/rucio && \
        cd /tmp/rucio && git checkout "${RUCIO_REF}" && \
        ./tools/build_sdist_wheel.sh rucio && \
        WHEEL=$(realpath dist/$(ls dist | grep -E '^rucio-.*\.whl' | head -n1)) && \
        python3 -m pip install --no-cache-dir \
            "rucio[${RUCIO_EXTRAS}] @ file://${WHEEL}" && \
        cd / && rm -rf /tmp/rucio && \
        dnf remove -y git && dnf autoremove -y && dnf clean all; \
    fi

but if we prefer to keep the Dockerfiles clean, we can either include this only as a suggestion (maybe inside some readme), or just have it here for reference in case it might give a clue to someone who is going to be needing this workaround in the future too.

An implementation can be found in Geogouz/containers.