Update jenkins for external docker use

Dockerfile

@@ -0,0 +1,20 @@
+FROM jenkins/jenkins:lts
+
+USER root
+
+# Docker dependencies
+RUN apt-get update && apt-get install -y \
+    apt-transport-https \
+    ca-certificates \
+    curl \
+    gnupg \
+    lsb-release
+
+# Add Docker repo
+RUN curl -fsSL https://download.docker.com/linux/debian/gpg | gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
+RUN echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian $(lsb_release -cs) stable" > /etc/apt/sources.list.d/docker.list
+
+# Install docker client
+RUN apt-get update && apt-get install -y docker-ce-cli
+
+USER jenkins