CB-10222 Add scaletype preference for Android splashscreen

[Sergey Shakhnazarov (Akvelon)]

Hi guys,

I wanted to discuss the SplashScreen plugin PR for Android adding ability to 
customize splash image scale type[1] to avoid its cutting.

Proposed solution is to make this an Android-preference like this:
    <preference name="SplashScaleType" value="CENTER_CROP|CENTER_INSIDE" />

Is there any suggestions on implementation or objections?

[1]: https://github.com/apache/cordova-plugin-splashscreen/pull/52

Best regards,
Sergey Shakhnazarov.