Add builder image, fix runners

docker/Dockerfile

@@ -0,0 +1,24 @@
+# Start from the same base as our target
+FROM ubuntu:24.04
+
+# Set non-interactive mode for apt to prevent it from asking questions
+ENV DEBIAN_FRONTEND=noninteractive
+
+# Update, install build tools, and install chrony's specific build-deps
+RUN apt-get update && \
+    apt-get install -y \
+    build-essential \
+    debhelper \
+    devscripts \
+    dpkg-dev \
+    git \
+    curl \
+    gnupg \
+    # Chrony's specific dependencies (from its debian/control file)
+    libcap-dev \
+    libedit-dev \
+    libgnutls28-dev \
+    libnss3-dev \
+    libseccomp-dev \
+    # Clean up apt cache
+    && rm -rf /var/lib/apt/lists/*