Improve documentation about SQL Server installation

## Description of documentation change
The documentation about installing SQL Server is good for developing purposes, but leaves a lot of "best practices" regarding performance and security issues.

Different use cases should also be considered:

* SQL Server on same machine as web server or not
* ~~Machine(s) is (are) domain members or not~~
* Installation inside a DMZ
* etc.

## Existing documentation URL
[Setting Up / DNNSet Up SQL on GitHub](https://github.com/DNNCommunity/DNNDocs/blob/master/content/administrators/setup/set-up-sql/index.md)
[Install and Setup SQL on DNNDocs](https://dnndocs.com/content/administrators/setup/set-up-sql/index.html)

## Existing documentation section (if applicable)

Whole page

## Proposed area for new documentation (if applicable)
Whole page