Use redis INCRBY and DECRBY when updating metrics values (#121)

Move test coverage processing to a seperate command

Use redis INCRBY and DECRBY when updating metrics values

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/121

Makefile

@@ -65,6 +65,9 @@ clean:
 .PHONY: test
 test:
 	VIKUNJA_SERVICE_ROOTPATH=$(shell pwd) go test $(GOFLAGS) -cover -coverprofile cover.out $(PACKAGES)
+
+.PHONY: test-coverage
+test-coverage: test
 	go tool cover -html=cover.out -o cover.html
 
 .PHONY: integration-test