feat: add filtering by container label for Docker integration (#194)

config.example.yaml

@@ -47,8 +47,14 @@ headscale:
 integration:
   docker:
     enabled: false
-    # The name (or ID) of the container running Headscale
-    container_name: "headscale"
+    # Preferred method: use container_label to dynamically discover the Headscale container.
+    container_label:
+      name: "com.headplane.selector"
+      value: "headscale"
+    # Optional fallback: directly specify the container name (or ID)
+    # of the container running Headscale
+    # container_name: "headscale"
+
     # The path to the Docker socket (do not change this if you are unsure)
     # Docker socket paths must start with unix:// or tcp:// and at the moment
     # https connections are not supported.