Add Docker configuration for (potential) use in Cabotage

Dockerfile.cabotage

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+# Adapted from https://github.com/buildbot/buildbot/raw/refs/heads/master/Dockerfile.master
+
+# Build the environment in an intermediate image, then copy it over to final.
+
+ARG DEBIAN_VERSION="trixie"
+
+FROM --platform=${BUILDPLATFORM} docker.io/library/debian:${DEBIAN_VERSION} AS buildbot-build
+
+RUN \
+    apt-get update && \
+    apt-get -y upgrade && \
+    apt-get -y install --no-install-recommends --no-install-suggests -q \
+        ca-certificates \
+        curl \
+        make \
+        git \
+        build-essential \
+        python3-dev \
+        virtualenv \
+        libpq-dev \
+        && \
+    rm -rf /var/lib/apt/lists/*
+
+# Copy requirements separately to avoid unnecessary rebuilds.
+COPY requirements*.txt /srv/buildbot/
+
+RUN virtualenv --python=python3 /srv/buildbot/venv && \
+    /srv/buildbot/venv/bin/pip3 install -r /srv/buildbot/requirements-*.txt
+
+COPY . /srv/buildbot
+
+# Copy docker-specific config into place
+COPY docker/buildbot.tac /srv/buildbot/master/buildbot.tac
+COPY docker/start_buildbot.sh /srv/buildbot/start_buildbot.sh
+
+
+#==============================================================================
+# Build the final image here.  Use build artifacts from the buildbot-build
+# container.
+
+FROM docker.io/library/debian:${DEBIAN_VERSION}-slim AS buildbot-master
+
+RUN \
+    apt-get update && \
+    apt-get -y upgrade && \
+    apt-get -y install -q \
+        curl \
+        dumb-init \
+        git \
+        libpq5 \
+        libcairo2 \
+        openssh-client \
+        python3 \
+        tar \
+        tzdata \
+        && \
+    rm -rf /var/lib/apt/lists
+
+COPY --from=buildbot-build /srv/buildbot /srv/buildbot
+
+WORKDIR /srv/buildbot
+CMD ["dumb-init", "/srv/buildbot/start_buildbot.sh"]

docker/buildbot.tac

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+import os
+import sys
+
+from twisted.application import service
+from twisted.logger import ILogObserver
+from twisted.logger import textFileLogObserver
+from twisted.logger import LogLevelFilterPredicate
+from twisted.logger import FilteringLogObserver
+
+from buildbot.master import BuildMaster
+
+basedir = os.environ.get("BUILDBOT_BASEDIR",
+    os.path.abspath(os.path.dirname(__file__)))
+configfile = 'master.cfg'
+
+# note: this line is matched against to check that this is a buildmaster
+# directory; do not edit it.
+application = service.Application('buildmaster')
+application.setComponent(
+    ILogObserver,
+    FilteringLogObserver(
+        textFileLogObserver(sys.stdout), predicates=[LogLevelFilterPredicate()]
+    ),
+)
+
+m = BuildMaster(basedir, configfile, umask=None)
+m.setServiceParent(application)

docker/start_buildbot.sh

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+#!/bin/bash
+
+# Adapted from https://github.com/buildbot/buildbot/raw/refs/heads/master/master/docker/start_buildbot.sh
+
+# startup script for purely stateless master
+
+export PATH="/srv/buildbot/venv/bin:$PATH"
+
+B=/srv/buildbot/master
+
+# Fixed buildbot master not start error in docker
+rm -f "$B/twistd.pid"
+# wait for db to start by trying to upgrade the master
+until buildbot upgrade-master "$B"
+do
+    echo "Can't upgrade master yet. Waiting for database ready?"
+    sleep 1
+done
+
+# we use exec so that twistd use the pid 1 of the container, and so that signals are properly forwarded
+exec twistd -ny "$B/buildbot.tac"