added subheading to review step for other contacts

src/registrar/assets/sass/_theme/_register-form.scss

@@ -78,3 +78,9 @@
   font-weight: font-weight('semibold');
   margin-bottom: units(0.5);
 }
+
+.review__step__subheading {
+  color: color('primary-dark');
+  font-weight: font-weight('semibold');
+  margin-bottom: units(0.5);
+}

src/registrar/templates/application_review.html

@@ -99,6 +99,7 @@
           {% if step == Step.OTHER_CONTACTS %}
             {% for other in application.other_contacts.all %}
               <div class="margin-bottom-105">
+                <div class="review__step__subheading">Contact {{ forloop.counter }}</div>
                 {% include "includes/contact.html" with contact=other %}
               </div>
             {% empty %}