Add toggle in settings page for Appearance

[AlaaElattar]

• Added toggle to switch between light and dark modes from settings page.
• If app is installed for the first time, the theme will be the systems's theme.

[AhmedHanafy725]

• The app doesn't fetch the initial state of the system
• On the dark mode the switch doesn't reach the end

[AlaaElattar]

[AhmedHanafy725]

Checking the brightness here will make the app start with one mode and not reflect when changing the system mode.

I prefer to return ThemeMode.system here and check the brightness before rendering the switch if the mode is the system.

[AhmedHanafy725]

Suggested change

	bool isSystemDarkMode = false;
	if (themeProvider.themeMode == ThemeMode.system){
	var brightness =
	SchedulerBinding.instance.platformDispatcher.platformBrightness;
	isSystemDarkMode = brightness == Brightness.dark;
	}
	bool isDarkMode = themeProvider.themeMode == ThemeMode.dark ||
	(themeProvider.themeMode == ThemeMode.system && isSystemDarkMode);
	bool isDarkMode;
	if (themeProvider.themeMode == ThemeMode.system){
	final brightness =
	SchedulerBinding.instance.platformDispatcher.platformBrightness;
	isDarkMode = brightness == Brightness.dark;
	} else {
	isDarkMode = themeProvider.themeMode == ThemeMode.dark;
	}