[Android] automatically configure Debug keystore if it's not configured

[sosasees]

suggested by @Calinou in godotengine/godot#76365 (comment):

A debug keystore can be generated by a single command, so I don't see much point in committing it to version control. In fact, it should probably be the Godot editor's job to automatically create this debug keystore and reference it in the Editor Settings when you try to export a project (if no debug keystore is currently configured).

[m4gr3d]

Fixed by godotengine/godot#90611