Allow automatic full invoice from API

[luigifab]

Description

This PR allow to full invoice an order from API, like you can already create full shipment or full credit memo.

$proxy = new SoapClient('...', ['trace' => 1, 'user_agent' => 'Local/Test']);
$sessionId = $proxy->login('covid', $pass);
var_dump($proxy->call($sessionId, 'sales_order.info', 'increment_id'));
var_dump($proxy->call($sessionId, 'sales_order_invoice.create', 'increment_id'));
var_dump($proxy->call($sessionId, 'sales_order_shipment.create', 'increment_id'));
var_dump($proxy->call($sessionId, 'sales_order_creditmemo.create', 'increment_id'));

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[tobihille]

Forgive me my ignorance but I don't see how your changes would allow full automatic invoice from api, there are only default values in functions added.
Can you please explain?

On the other hand: I don't see how your changes could harm anything.

[luigifab]

Because this is the default behaviour of prepareInvoice:

magento-lts/app/code/core/Mage/Sales/Model/Service/Order.php

Lines 104 to 112 in e6e5ad7

	/**
	* Prepare order invoice based on order data and requested items qtys. If $qtys is not empty - the function will
	* prepare only specified items, otherwise all containing in the order.
	*
	* @param array $qtys
	* @return Mage_Sales_Model_Order_Invoice
	*/
	public function prepareInvoice($qtys = [])
	{

[fballiano]

I also fail to understand (at first sight) how adding only the default value for the qtys fixes it (but didn't have time to actually test)

[github-actions]

Unit Test Results

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
0 tests ±0  0 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
7 runs  ±0  5 ✔️ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit 52f2c75. ± Comparison against base commit 01edaf6.