gettext-template: Update POTFILES if there are removed or added files that includes translatable strings

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

## Feature
**Is your feature request related to a problem? Please describe.**
Editing POTFILES is not automated at the moment, so if we forget to update POTFILES when adding/removing files that include translatable strings, Gettext Actions will fail.

**Describe the solution you'd like**
It would be useful if the Gettext Actions can detect added/removed files from a project, check if they include translatable strings (`_()`, `ngettext ()`, `dgettext ()`, etc.), and if so remove/add the path to them from POTFILES automatically.

**Existing work**
N/A

**Describe alternatives you've considered**
N/A

**Additional context**
N/A