feat: add feature to load data from file

[legosandorigami]

Hi, this pull request solves issue #3. I considered modifying the file watcher to monitor changes in the data file as well, However, I decided against this, as changes to the data can be made directly through the UI (index.html). These updates are automatically reflected in the template via the /data endpoint handled by handleUpdateTemplateData handler.

I apologize for the mistakes in advance.