### Godot version

3.5.1.stable, v4.0.beta.custom_build [0a87ead64]

### System information

Ubuntu 22.04.1

### Issue description

For example, if project has name "300spartans", we can't enter the "org.godotengine.300spartans" to "Unique Name" field. We get the error "Invalid package name: A digit cannot be the first character in a package segment". But , if we enter "org.godotengine.$genname", there will be no error message. When exporting, the name will be set as "org.godotengine.spartans" without "300" in beginning, but user will not be informed about it. I think, it is not very good. It may not be worth making changes to the source code, but mention it in the documentation.

### Steps to reproduce

See issue description.

### Minimal reproduction project

N/A
Vector<PluginConfigAndroid> loaded_plugins;
	String plugins_dir = ProjectSettings::get_singleton()->get_resource_path().path_join("android/plugins");
	
	loaded_plugins.append_array(PluginConfigAndroid::get_prebuilt_plugins(plugins_dir));
	if (DirAccess::exists(plugins_dir)) {
		Vector<String> plugins_filenames = list_gdap_files(plugins_dir);
		if (!plugins_filenames.is_empty()) {
			Ref<ConfigFile> config_file = memnew(ConfigFile);
			for (int i = 0; i < plugins_filenames.size(); i++) {
				PluginConfigAndroid config = PluginConfigAndroid::load_plugin_config(config_file, plugins_dir.path_join(plugins_filenames[i]));
				if (config.valid_config) {
					loaded_plugins.push_back(config);
				} else {
					print_error("Invalid plugin config file " + plugins_filenames[i]);
				}
			}
		}
	}
	return loaded_plugins;
}
Vector<PluginConfigAndroid> EditorExportPlatformAndroid::get_enabled_plugins(const Ref<EditorExportPreset> &p_presets) {