enable CI cache

.gitlab-ci.yml

@@ -1,6 +1,7 @@
 variables:
   RUST_IMAGE: "rust:latest"
   NODE_IMAGE: "node:lts"
+  CARGO_HOME: $CI_PROJECT_DIR/cargo
 
 stages:
   - lint
@@ -8,6 +9,13 @@ stages:
   - test
   - release
 
+cache:
+  key: ${CI_COMMIT_REF_SLUG}
+  paths:
+    - target
+    - cargo
+    - ui/node_modules
+
 lint:backend:
   stage: lint
   image: $RUST_IMAGE