Configure deployment to Google Play Alpha track

[Humorloos]

• [x] set up alpha track in google play console
• [x] use "need icon" icon
• [x] use empty preview image
• [x] use empty splash screen: see https://www.joshmorony.com/adding-icons-splash-screens-launch-images-to-capacitor-projects/
• [ ] configure automatic publishing in alpha track in pipeline
  • this has to be a separate deployment action to internal, not replace it
  • see #303
• [x] #403