Add kits subfolder to allow for multiple kit files

[GenSecrets]

Information

Details

Proposed feature:

Add to the existing kits system (not overhaul) and allow for server owners to have the option of separating kits out into individual files for storage or organization purposes. The separated kits would be stored in a folder aptly named "kits", inside of the Essentials data folder (Essentials/kits)

• Kit files follow same format as the kits.yml
• The kits.yml has not been changed, must still stay in the main Essentials directory
• A config option has been added to config.yml called "use-kits-subfolder" which defaults to false. Can be set to true if server owner wishes for the folder to be created and parsed. If false, any files in the folder will not be read by the plugin (or loaded, to save memory).
• Plugin will skip all files that aren't .yml files, and if the yml files do not contain a "kits" section, it will throw an error in the console and alert the server owner to which file is incorrectly defined

The driving factor behind this is that our large server network has held a custom fork of ESSX for this for years, and the sole reason of us updating our own fork is simply for a kits subfolder. I ran a count and of all parsed kits we have around 1400 it seems, and the kits file would be absolutely tremendous and a nightmare to sort through. It still is sometimes cause it's still tens of thousands of lines long on its own. However in the kits folder we keep them organized based on many factors; kits based on classes, spells, food, donor items, etc, you name it. 208 files and counting in the folder. We are looking to get rid of how many custom plugins or forks we're having to constantly maintain and upkeep at the slightest server version change so I'm creating this PR because I know it will help us tremendously and if it's helped us (and my brain for sake of organization) then I know it's bound to help someone else.

Note: I'm no pro with Configurate, so should something in the format have the chance to be better optimized, please do advise. Thanks!

Environments tested:

OS:
Developed on Windows (x64, using IntelliJ Idea, jdk 1.16)
Tested on Linux (amd64, 8 cores, 1.8.0 java built 11)

Java version:
16.0.2

• 16 Paper version (1.16.5, git-Paper-783)
• Airplane (1.16.5, git-Airplane-9f0a29b)
• CraftBukkit/Spigot/Paper 1.12.2
• CraftBukkit 1.8.8

Demonstration:

• If a player wishes to enable this, they can turn it on in config.yml via enabling the new option "use-kits-subfolder" and setting it to "true" (default is false). Once true, it will create a kits folder as seen in the picture below
  

[GenSecrets]

This would in part resolve some (but not all) of #3944

re-review pending

[JRoy]

Thanks for your contribution!