✨ Custom Templates for Index files

[DJmouton]

Describe the solution you'd like
Being able to use a custom template for index files, the same way you can with other notes.
For example:
"template" : {
"index" : "ttrpg-convert-cli-main/examples/templates/tools5e/index.txt"
}

Describe alternatives you've considered
I saw there's already a default template used for index files, I modified it but since I currently didn't have the workspace to rebuild the project it didn't do anything.