[FR] Allow only `ItemsAdder/contents/` and `contents/` folder structures for saving an entity

[Andre601]

Is your feature request related to a problem? Please describe.
The plugin currently requires the iaentity file to be saved in a plugins/ItemsAdder/contents/<namespace>/ directory, which is rather tedious for when you save your project outside of your server.

Describe the solution you'd like
The plugin should accept and recognize ItemsAdder/contents/<namespace>/ and also contents/<namespace>/ folders as valid directories to allow easier storing of data.

Describe alternatives you've considered
Creating the folder structure the plugin demands.

Additional context