Introducing the Advanced Administration handbook

During the recategorization of the documentation, the team removed several articles that were developer-focused or included a lot of developer-jargon. All these articles are now part of the Advanced Administration Handbook and will be removed from /documentation/devhub/.

The redirects have been applied as indicated in issue #59. Some articles have been merged to provide better explanations. Although, the maintenance is still ongoing, most of the articles have been updated.

Please report any issues to the documentation GitHub issue tracker.

Props to @ryelle and @javiercasares for working on this issue.