Submit the guest order tracking form with POST

[boo-code]

Questions	Answers
Description?	The guest order tracking form is submitted with GET, so the shopper's email address ends up in the URL. It is then recorded by analytics as a page path, kept in the browser history, and written to the access log and any referrer. Submitting it with POST keeps the address out of the URL.
Type?	bug fix
BC breaks?	no
Deprecations?	no
Fixed ticket?	PrestaShop/PrestaShop#13911
Sponsor company	-
How to test?	See below.

Why

templates/customer/guest-login.tpl submits the tracking form with method="get", and the form holds a
field named email. Submitting it therefore produces a URL of the shape
/guest-tracking?order_reference=...&email=someone@example.com.

That is the report in PrestaShop/PrestaShop#13911: email addresses visible in Google Analytics page
paths. A URL carrying the address does not only reach analytics — it is also kept in the browser history,
written to the web server access log, and sent as the referrer to anything the page loads.

What it does

Switches the form to method="post".

Tools::getValue() reads $_POST before $_GET (classes/Tools.php), and GuestTrackingController
reads order_reference and email through it, so no controller change is needed. Links that already
carry the parameters in a query string keep working, since the controller still accepts them.

The hidden controller input is left in place. It exists because a GET form replaces the action's query
string with its own fields; with POST the action's query string is preserved and the input is simply
harmless.

How to test

1. Front office, open the guest order tracking page.
2. Fill in an order reference and an email, submit.
3. Before: the address bar shows ...&email=someone@example.com. After: the URL carries no email.
4. A link that already carries ?order_reference=...&email=... still resolves the order.