Better support for 24 and 12 hour time formats (#52)

[Aga-C]

What is it?

• [ ] Bugfix
• [x] Feature
• [ ] Codebase improvement

Description of the changes in your PR

• Added zero padding for hour in 24-hour digital clock (both app and widget), because it's a standard formatting.
• Added AM/PM indicator in 12-hour digital clock widget.
• Added switch between 12 and 24-hour time formats.
  • Original issue was mentioning this kind of switch, and since it's already in Calendar, it could be also done here.
  • By default, it uses system time format.
  • It works for all clocks in the app and for digital clock widget.

Before/After Screenshots/Screen Record

https://github.com/FossifyOrg/Clock/assets/85929121/36c6f008-30f3-405d-a8d5-74295d239996

Fixes the following issue(s)

• Fixes #52

Acknowledgement

• [x] I read the contribution guidelines.

[frobby]

May I suggest adding a setting for a custom date/time format? Using format codes such as these eg: I would like to change the date format to: "Mon 02 Sep" instead of "Mon, 2 Sept"

[Joshix-1]

The switch between the formats should imho have 3 states: system default, 12h format and 24h format

[naveensingh]

Thanks :)