Firest draft of the "How to Organize Configuration Files" cookbook
Added all the suggestions made by reviewers
Added the latest suggestions made by reviewers
Fixed the link to another cookbook article
Added suggestions made by @cordoval
Fixed the target of one cookbook article link
Removed the "Directory Loading" section because it doesn't work out of the box
Added more suggestions made by @xabbuh
Removed redundant configuration blocks
feature #3885 [RFR] Added "How to Organize Configuration Files" cookbook (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
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[RFR] Added "How to Organize Configuration Files" cookbook

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3680

This is just the first draft of a new cookbook. Please, tell me anything that I should add, change or remove. Thanks!

Commits
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4241ee5 Removed redundant configuration blocks
68a7d2a Added more suggestions made by @xabbuh
be414e0 Removed the "Directory Loading" section because it doesn't work out of the box
da3e1d0 Fixed the target of one cookbook article link
af5d478 Added suggestions made by @cordoval
4a87cfb Fixed the link to another cookbook article
2a32b23 Added the latest suggestions made by reviewers
d861be3 Added all the suggestions made by reviewers
0520bf1 Firest draft of the "How to Organize Configuration Files" cookbook