Switch agent over to jenkins/agent

We haven't been using the old agent, so repurpose this to use as a signing agent.

Dockerfile

@@ -1,38 +1,26 @@
-FROM jenkins/ssh-agent:jdk11
+FROM jenkins/agent:3148.v532a_7e715ee3-2-jdk17
+
+ARG user=jenkins
+
+USER root
+
 RUN apt-get update && \
     apt-get install --yes --no-install-recommends \
-    libfreetype6 \
-    fontconfig \
-    fonts-dejavu \
     git \
     gnupg \
     ca-certificates \
     curl \
-    tigervnc-standalone-server \
-    tigervnc-common \
-    fluxbox \
-    libfontconfig \
-    libglu1 \
-    libnss3 \
-    libxcomposite1 \
-    libxcursor1 \
-    libpulse0 \
-    libasound2 \
-    libtinfo5 \
-    libx11-6 \
-    libxcb1 \
-    libxdamage1 \
-    libxi6 \
-    libxext6 \
-    libxfixes3 \
-    libxtst6 \
     zlib1g \
-    libgl1
-RUN curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg | gpg --dearmor -o /usr/share/keyrings/githubcli-archive-keyring.gpg && \
-    echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" | tee /etc/apt/sources.list.d/github-cli.list && \
-    apt-get update && \
-    apt-get install --yes --no-install-recommends gh
-RUN mkdir /home/jenkins/.vnc && \
-    (echo jenkins; echo jenkins; echo "n") | vncpasswd /home/jenkins/.vnc/passwd && \
-    chown -R jenkins /home/jenkins
-RUN groupadd -g 102 -r kvm && usermod -aG kvm jenkins
+    unzip \
+    wget \
+    jq \
+    python3-venv \
+    python3-pip
+
+RUN curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg | dd of=/usr/share/keyrings/githubcli-archive-keyring.gpg \
+    && chmod go+r /usr/share/keyrings/githubcli-archive-keyring.gpg \
+    && echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" | tee /etc/apt/sources.list.d/github-cli.list > /dev/null \
+    && apt-get update \
+    && apt-get install -y --no-install-recommends gh
+
+USER ${user}