Specify filename mode manually

Steps to reproduce

1. Go to filename mode in settings
2. Choice is to either use original file name or not

Expected behaviour

User should have the ability to select their own file name. Moreover, as most of the backends are Linux, having spaces between date, time, and trailing digits create problems

Actual behaviour

Let the user select the format or use the more conventional format date_time_single trailing digit

Reasoning or why should it be changed/implemented?

Increases the readability, clears any potential issues having spaces between date, time, and trailing digits

Environment data

iOS version:
15.6
Apples to every version

Nextcloud iOS app version: see More > Settings
4.4.0.18
Applies to every version that has this feature

Server operating system:
Debian 11

Web server: Apache, nginx
NA

Database:
NA

PHP version:
NA

Nextcloud version: see Nextcloud admin page
NA

Start in the iOS app's filename mode settings and trace how the selected mode reaches filename generation. Done means users can choose a filename format, including a conventional date_time_single-trailing-digit form, and filenames avoid spaces that cause backend issues.