Add Dockerfile to build tailscale docker image for integration tests

Dockerfile.tailscale

@@ -0,0 +1,9 @@
+FROM ubuntu:latest
+
+RUN apt-get update \
+    && apt-get install -y gnupg curl \
+    && curl -fsSL https://pkgs.tailscale.com/stable/ubuntu/focal.gpg | apt-key add - \
+    && curl -fsSL https://pkgs.tailscale.com/stable/ubuntu/focal.list | tee /etc/apt/sources.list.d/tailscale.list \
+    && apt-get update \
+    && apt-get install -y tailscale \
+    && rm -rf /var/lib/apt/lists/*