Add "validate" target

Author: glensc

Makefile

@@ -8,8 +8,11 @@ release: bump-interdependency
 bump-interdependency: monorepo-builder
 	monorepo-builder/bin/monorepo-builder bump-interdependency "^$(VERSION)"
 
+validate: monorepo-builder
+	monorepo-builder/bin/monorepo-builder validate
+
 split: monorepo-builder
 	monorepo-builder/bin/monorepo-builder split --max-processes=1 --tag=$(VERSION)
 
 monorepo-builder:
-	composer create-project symplify/monorepo-builder $@
+	composer create-project symplify/monorepo-builder $@ --keep-vcs --prefer-source --no-install