fix vettool; run vet on all available packages (#10389)

#### Summary
Unfortunately, `which shadow` didn't resolve to the shadow binary, so hard-code the expected path in `$GOPATH/bin`. At the same time, run `go vet` across both the server and enterprise (if present), reducing the number of required invocations.

This is accompanied by an enterprise change to fix shadowing issues there.

#### Ticket Link
N/A (tooling upgrade)

#### Checklist
- [x] Has enterprise changes: https://github.com/mattermost/enterprise/pull/403

Makefile

@@ -290,14 +290,9 @@ clean-docker: ## Deletes the docker containers for local development.
 
 govet: ## Runs govet against all packages.
 	@echo Running GOVET
-	$(GO) get -u golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow
-	$(GO) vet $(GOFLAGS) $(TE_PACKAGES) || exit 1
-	$(GO) vet -vettool=$(which shadow) $(GOFLAGS) $(TE_PACKAGES) || exit 1
-
-ifeq ($(BUILD_ENTERPRISE_READY),true)
-	$(GO) vet $(GOFLAGS) $(TE_PACKAGES) || exit 1
-	$(GO) vet -vettool=$(which shadow) $(GOFLAGS) $(EE_PACKAGES) || exit 1
-endif
+	$(GO) get golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow
+	$(GO) vet $(GOFLAGS) $(ALL_PACKAGES) || exit 1
+	$(GO) vet -vettool=$(GOPATH)/bin/shadow $(GOFLAGS) $(ALL_PACKAGES) || exit 1
 
 gofmt: ## Runs gofmt against all packages.
 	@echo Running GOFMT