I'm using custom build of Godot 3.5 with custom built export templates. I can export Android .APK. Now I want to export .AAB (required for Google Play). But this requires me to "install Android build template" from the "Project" menu. The "Manage Templates" within this is unable to get list of mirrors, presumably because I'm using a custom build. So, how do I make my own "Android build template" or where do I get one? There's nothing in the "Custom builds for Android" or "Exporting for Android" documentation pages that tells me this. I've found out that it should be "android_source.zip" but I have not been able to find out where to get that or, even better, how to build it myself.