[FIX] web: prevent iOS from zooming in on input fields

When a user clicks on an input or a select field
in Safari on IOS, Safari has a behavior of zooming-in
on the field when the keyboard opens.
Even after the user dismisses the keyboard, the screen
still stays zoomed-in. The user has to then zoom out manually.

Now, the user is not allow to zoom-in at all.
This is already the case with the Android application.
We now have the same behavior between the two apps.

addons/web/views/webclient_templates.xml

@@ -193,7 +193,7 @@
             <head>
                 <meta charset="utf-8"/>
                 <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"/>
-                <meta name="viewport" content="width=device-width, initial-scale=1"/>
+                <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"/>
 
                 <title t-esc="title or 'Odoo'"/>
                 <link type="image/x-icon" rel="shortcut icon" t-att-href="x_icon or '/web/static/src/img/favicon.ico'"/>