A basis template to develop Godot Android plugins, with a working directory structure.
As a starting point take a look at CustomSingleton.java class.
See https://godotengine.org/article/godot-3-2-will-get-new-android-plugin-system for instructions, and also https://docs.godotengine.org/en/latest/tutorials/plugins/android/android_plugin.html for how to create a plugin.
Other links: https://docs.godotengine.org/en/latest/getting_started/workflow/export/android_custom_build.html