After some self-testing, I figured out how to add name attribute to form tag.
All I did is to add html_name=”form-name”, to form’s shortcode. Now I get
<form name=”form-name” action=”/contact/#wpcf7-f91-o2″ method=”post” class=”wpcf7-form” novalidate=”novalidate”>.
But I still need help to add custom attributes to form fields…