Makefile: add linting and testing for submodules (#59)

Makefile

@@ -135,15 +135,17 @@ endif
 
 .PHONY: lint
 lint: agentlint
-	golangci-lint run -v --timeout=10m
+	find . -name go.mod -execdir golangci-lint run -v --timeout=10m \;
 	$(AGENTLINT_BINARY) ./...
 
 .PHONY: test
 # We have to run test twice: once for all packages with -race and then once
-# more without -race for packages that have known race detection issues.
+# more without -race for packages that have known race detection issues. The
+# final command runs tests for all other submodules.
 test:
 	$(GO_ENV) go test $(GO_FLAGS) -race $(shell go list ./... | grep -v /integration-tests/)
 	$(GO_ENV) go test $(GO_FLAGS) ./internal/static/integrations/node_exporter ./internal/static/logs ./internal/component/otelcol/processor/tail_sampling ./internal/component/loki/source/file ./internal/component/loki/source/docker
+	$(GO_ENV) find . -name go.mod -not -path "./go.mod" -execdir go test -race ./... \;
 
 test-packages:
 	docker pull $(BUILD_IMAGE)