OpenAPI Mattermost Go Vet integration (#14216)

* integrating govet
* added api spec check to CI

Makefile

@@ -517,9 +517,14 @@ vet: ## Run mattermost go vet specific checks
 	@if ! [ -x "$$(command -v $(GOBIN)/mattermost-govet)" ]; then \
 		echo "mattermost-govet is not installed. Please install it executing \"GO111MODULE=off GOBIN=$(PWD)/bin go get -u github.com/mattermost/mattermost-govet\""; \
 		exit 1; \
+	fi;
+	@VET_CMD="-license -structuredLogging -inconsistentReceiverName -tFatal"; \
+	if ! [ -z "${MM_VET_OPENSPEC_PATH}" ] && [ -f "${MM_VET_OPENSPEC_PATH}" ]; then \
+		VET_CMD="$$VET_CMD -openApiSync -openApiSync.spec=$$MM_VET_OPENSPEC_PATH"; \
+	else \
+		echo "MM_VET_OPENSPEC_PATH not set or spec yaml path in it is incorrect. Skipping API check"; \
 	fi; \
-
-	$(GO) vet -vettool=$(GOBIN)/mattermost-govet -license -structuredLogging -inconsistentReceiverName -tFatal ./...
+	$(GO) vet -vettool=$(GOBIN)/mattermost-govet $$VET_CMD ./...
 ifeq ($(BUILD_ENTERPRISE_READY),true)
 ifneq ($(MM_NO_ENTERPRISE_LINT),true)
 	$(GO) vet -vettool=$(GOBIN)/mattermost-govet -enterpriseLicense -structuredLogging -tFatal ./enterprise/...