Reduce CI go module downloads, add make targets (#18708)

The CI currently downloads all go modules in each pipeline step because
go modules reside outside the project directory. Fix this by introducing
a volume for the `/go` directory [1] so modules are only downloaded once per
pipeline using a new `deps-backend` make target.

For completeness, I also included new `deps` and `deps-frontend` targets
and the frontend one is also triggered explicitly on CI where needed.

[1] https://docs.drone.io/pipeline/kubernetes/examples/language/golang/#dependencies

.golangci.yml

@@ -24,6 +24,10 @@ linters:
 
 run:
   timeout: 3m
+  skip-dirs:
+    - node_modules
+    - public
+    - web_src
 
 linters-settings:
   gocritic:

Makefile

@@ -166,6 +166,9 @@ help:
 	@echo " - watch-backend                    watch backend files and continuously rebuild"
 	@echo " - clean                            delete backend and integration files"
 	@echo " - clean-all                        delete backend, frontend and integration files"
+	@echo " - deps                             install dependencies"
+	@echo " - deps-frontend                    install frontend dependencies"
+	@echo " - deps-backend                     install backend dependencies"
 	@echo " - lint                             lint everything"
 	@echo " - lint-frontend                    lint frontend files"
 	@echo " - lint-backend                     lint backend files"
@@ -662,6 +665,16 @@ docs:
 	fi
 	cd docs; make trans-copy clean build-offline;
 
+.PHONY: deps
+deps: deps-frontend deps-backend
+
+.PHONY: deps-frontend
+deps-frontend: node_modules
+
+.PHONY: deps-backend
+deps-backend:
+	$(GO) mod download
+
 node_modules: package-lock.json
 	npm install --no-save
 	@touch node_modules