Pre-populate new files from template

[gamberoillecito]

Description

Add an option so that whenever a user creates a new file, instead of being an empty file, it has some customizable predefined content. Similarly to what can be done in Obsidian: https://help.obsidian.md/Plugins/Templates

Use Case

The reason why I think this would be helpful is that in typst it is not possible to use functions (and similar) defined in the parent file in a child file. This requires to define all functions in a separate file (e.g. global_funcs.typ) and import it in every new file.

In the way I structure my projects (one file per chapters), it becomes annoying to always have to copy-paste the same import line.

Although this is the use case that prompted me to open this issue, I am sure there are many other similar cases (such as creating a new chapter with predefined headings and so on).