Add empty states [CLI-33]

[Widcket]

Description

This PR adds empty states for apps, apis, and rules. Also refactors the heading display logic to always include the current active tenant, to avoid having to copy and paste it everywhere. And adds the heading to the output of a command that was missing it (tenants list).

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[cyx]

Thank you!