Update all `package.json` descriptions

[andyleejordan]

Prerequisites

• I have written a descriptive issue title.
• I have searched all issues to ensure it has not already been reported.

Summary

Quite a few of our setting and command descriptions in package.json, for instance:

        "powershell.scriptAnalysis.enable": {
          "type": "boolean",
          "default": true,
          "description": "Enables real-time script analysis from PowerShell Script Analyzer. Uses the newest installed version of the PSScriptAnalyzer module or the version bundled with this extension, if it is newer."
        },

is totally wrong.

I was about to fix just this, but then was looking through and most if not all of these should be reviewed and updated. Furthermore, it would be a great improvement to switch to markdownDescription and have proper links to mentioned settings, etc.

Proposed Design

No response