Update incrementing logic to as to preserve filenames already ending with a number

[josephtribulat]

Right now, when a template choice is set to "increment" in case the file already exists, it creates a new file with the same name followed by a number. But when the original filename already ends with a number, it increments that number. For example if it's a journal entry like 2024-06-14.md, the new file will be called 2024-06-15.md. This leads to some confusion.

Shouldn't it rather be something like 2024-06-14-1.md?