Change the spinner position on the Splash Screen

## Feature Request

### Plugin
Capacitor 3 Splash Screen

### Description
Splash screen typically have a logo or other feature in the center of the screen. Currently the spinner on the Splash Screen plugin is fixed to the center horizontally and vertically. Being able to configure the spinner to appear elsewhere on the screen would be useful.

### Platform(s)
iOS
Android

### Preferred Solution
Add an option to capacitor.config.json to determine the position of the spinner, ie TOP CENTER, MIDDLE CENTER, BOTTOM CENTER, TOP LEFT, etc.

### Alternatives
i've achieved this on iOS by changing Pods > Development Pods > Capacitor > Plugins > SplashScreen.swift lines 128 and 164 from
`self.spinner.centerYAnchor.constraint(equalTo: view!.centerYAnchor).isActive = true`
to
`self.spinner.bottomAnchor.constraint(equalTo: view!.safeAreaLayoutGuide.bottomAnchor).isActive = true`

This moves it to the bottom center - the addition of the .safeAreaLayoutGuide ensures it doesn't cover the gesture bar on iPhone 10+

I don't have a solution for Android yet, but Google searching suggests that can be changed in the .java file also.

### Additional Context
Based on a post here [https://github.com/ionic-team/capacitor/discussions/3508](https://github.com/ionic-team/capacitor/discussions/3508) and the suggestion to post this as a feature request.