added Dockefile and entrypoint.sh

It uses the latest available version for libtorrent and builds both libtorrent and qBittorrent with Cmake + ninja

The legal notice must be accepted trought an environment variable called LEGAL and passed to docker when the container is run, to set it true one must set "LEGAL=accept"

PR #16828.

dist/docker/Dockerfile

@@ -0,0 +1,37 @@
+
+FROM alpine:latest AS builder
+
+ARG BUILD_TYPE
+ARG RELEASE
+
+RUN if [ $RELEASE = "master" ] ; \
+    then \
+      wget https://github.com/qbittorrent/qBittorrent/archive/refs/heads/master.zip && \
+      unzip master.zip && \
+      cd qBittorrent-master ; \
+    else \
+      wget https://github.com/qbittorrent/qBittorrent/archive/refs/tags/release-${RELEASE}.tar.gz && \
+      tar xf release-${RELEASE}.tar.gz && \
+      cd qBittorrent-release-${RELEASE} ; \
+    fi && \
+    apk add --no-cache qt6-qttools-dev g++ libtorrent-rasterbar-dev cmake boost-dev ninja && \
+    cmake -B build-nox -G "Ninja" -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DGUI=OFF -DQT6=ON -DSTACKTRACE=OFF && \
+    cmake --build build-nox && \
+    cmake --build build-nox --target install/strip
+
+FROM alpine:latest
+
+COPY --from=builder /usr/local/bin/qbittorrent-nox /usr/bin/qbittorrent-nox
+
+COPY entrypoint.sh /entrypoint.sh
+
+RUN chmod +x /entrypoint.sh && \
+    apk add --no-cache qt6-qtbase libtorrent-rasterbar
+
+ENV WEBUI_PORT="8080"
+
+EXPOSE 6881 6881/udp 8080
+
+VOLUME /config /downloads
+
+ENTRYPOINT ["/entrypoint.sh"]