Use docker on CI

Dockerfile.builder

@@ -0,0 +1,17 @@
+# SRFPlay Builder Image
+# Pre-built image with .NET SDK and JPRM for building Jellyfin plugins
+# Build: docker build -f Dockerfile.builder -t gitea.tourolle.paris/dtourolle/srfplay-builder:latest .
+# Push:  docker push gitea.tourolle.paris/dtourolle/srfplay-builder:latest
+
+FROM mcr.microsoft.com/dotnet/sdk:8.0
+
+RUN apt-get update && apt-get install -y \
+    python3 \
+    python3-pip \
+    git \
+    jq \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN pip install --break-system-packages jprm
+
+WORKDIR /src