feat: custom package path

[d-kaue]

Closes #52. Currently only works on the Desktop app due to #38.

If Use custom package path is checked, the user have to choose a path and click on the save button.
If the user reloads without saving, the path will be the default packages/ in the vault root.

• Pros:
  • Possibility to read the README.md of each package.
  • Possibility to read each .typ in the future when Custom editor for .typ files works. (currently can be shown only in the file tree if Detect all file extensions is enabled on Files and links settings)
• Cons:
  • These folders will be visible on the Quick Switcher, if we have many folders this could be annoying, but is up to the user to use this option.

This feature doesn't require reload.

I'm not fluent in English, please let me know if there any typos.