Story (Required)

As a developer, I want to be able to disable the default menu items in RHDH if I am setting up a custom instance of RHDH like Sandbox.

Background (Required)

We want to use RHDH for Sandbox landing page. So we want to customize the current RHDH sidebar navigation and disable the default menu items.

Acceptance Criteria (Required)

• Should use the app-config to override/disable the default menu items in RHDH.
• Should make use of the `default.main-menu-item` config from https://github.com/redhat-developer/rhdh/blob/main/packages/app/src/App.tsx#L17.
• Should find out why the override doesn't work right now and fix the issue or introduce the ability.