Adding support for MacOs

[rwaal]

This PR adds support for MacOs for the AIPAS IPAM solution.

Changes

Most notable changes are in the README file:

• Added instructions for installing prerequisites for MacOs. Moved the prereq installation instructions to separate markdown file to keep main README uncluttered.
• Changed the PowerShell code in the README for cross platform support. Out-GridView is Windows-only, so needed to be replaced. I realise that manually entering a subscriptionId is not as elegant as using Out-GridView, but this at least works on all systems.
• Replaced the code that writes app settings to environment variables. The original code will not work on Mac and Linux. I choose to write the app settings to the local.settings.json file, which will work on all supported OS'es, and is a common way to store app settings for local development.

tasks.json file:

• Added alternative commands for MacOs. The original command will only work on Windows. The "osx" commands will automatically be executed on a MacOs system.