Monochrome icon

[xmha97]

Please support the Android 13+ themed app icon feature.

[jmattheis]

There were some tries for monochrome icons in gotify/logo#3 for the notification icon, but we then settled on https://github.com/gotify/logo/blob/master/gotify-logo-notification.png for the icon.

If someone wants to contribute a monochrome icon that's the similar to the current app icon I'm open for pull requests in gotify/logo.