feat: add keepdeps.go to preserve mod clean in opensource version (#11752)

* feat: add keepdeps.go to preserve enterprise-only dependencies in OSS builds

* feat: migrate keepdeps.go to core/deps for OSS builds

Author: HynoR

core/deps/keepdeps.go

@@ -0,0 +1,9 @@
+//go:build !xpack
+
+package deps
+
+// Keep xpack deps from being pruned by go mod tidy
+import (
+	_ "github.com/patrickmn/go-cache"
+	_ "github.com/pkg/sftp"
+)