Update docs to increase visibility of setup guide

🎯 Aim

The aim of this issue is to update our guidance to make the basic install + setup + login really clear and a step by step path. The initial setup, so when we use m365 setup command or, since not everybody can use this option, we need to add the app reg manually, is a must have before we start using CLI for Microsoft 365. From our docs it is not that obvious and easy to find guide. It is not even in the top 3 guides in our docs 🤔. I suggest we do the following to make this all easier for our users.

1. first of all let's add a new group in our docs "Getting Started" and in this group add the following:
   1. "Overview" page - this is a new page in which we do a high level explanation of what needs to be done with the 'happy' path easiest steps to get started. Like how to install using npm, how to setup using the setup command and the initial login. If someone wants to use yarn for installing or docker or adding the app reg manually then for those scenarios we provide links to the following next pages mentioned below which provide more content.
   2. Next page is the install guide - as we have now
   3. then we add the setup guide next with name 'Setup the CLI'
   4. then we reorder and show the 'Log in to Microsoft 365' page
2. then we go with 'Use the CLI'
3. . ... then everything else as we have now

Also we should refactor the 'Use your own Microsoft Entra identity' content. The content is generally ok and well written. I would only refactor it a bit describing this is an obligatory step everyone need to perform in order to use CLI for Microsoft 365

📸 Expected result

Suggested menu order

1. Getting Started
    1. Overview ----> new page 
    2. Install the CLI
    3. Setup the CLI ----> old/new page
    4. Log in to Microsoft 365
2. Use the CLI
3. .... all other