"External Dependency Manager" menu option missing

### Please fill in the following fields:
Unity editor version: 2019.3.6f1
External Dependency Manager version: 1.2.144
Features in External Dependency Manager in use (Android Resolver, iOS Resolver, VersionHandler, etc.): -
Plugins SDK in use (Firebase, Admob, Facebook, etc.): Facebook, Firebase
Platform you are using the Unity editor on (Mac, Windows, or Linux): Windows
Platform you are targeting (iOS, Android, and/or desktop): Android
Scripting Runtime (Mono, and/or IL2CPP): IL2CPP

### Please describe the issue here:

1. Install External Dependency Manager unitypackage.

**Expected result:**

> EDM4U adds the registry to Packages/manifest.json under your current Unity project folder.

> You can also manaully add this registry later using the Assets > External Dependency Manager > Unity Package Manager Resolver > Add Registries or Window > Google > Game Package Registry > Add To Project menu options.

As per https://firebase.google.com/docs/unity/setup#add-sdks-upm

**Actual result:**

There's no "External Dependency Manager" optin in "Assets" menu.

### Please answer the following, if applicable:
What's the issue repro rate? (eg 100%, 1/5 etc) 100%