Split SubscriptionForm into SubscriptionNewUserForm and SubscriptionExistingUserForm

subscription/templates/subscription/fragments/creation_form.jinja

@@ -0,0 +1,10 @@
+<form
+  hx-post="{{ post_url }}"
+  hx-target="this"
+  hx-disabled-elt="find input[type='submit']"
+  hx-swap="outerHTML"
+>
+  {% csrf_token %}
+  {{ form.as_p() }}
+  <input type="submit" value="{% trans %}Save{% endtrans %}">
+</form>

subscription/templates/subscription/fragments/creation_success.jinja

@@ -0,0 +1,27 @@
+<div class="alert alert-green">
+  <div class="alert-main">
+    <h3 class="alert-title">
+      {% trans user=subscription.member %}Subscription created for {{ user }}{% endtrans %}
+    </h3>
+    <p>
+
+      {% trans trimmed user=subscription.member.get_short_name(), type=subscription.subscription_type, end=subscription.subscription_end %}
+        {{ user }} received its new {{ type }} subscription.
+        It will be active until {{ end }} included.
+      {% endtrans %}
+    </p>
+  </div>
+  <div class="alert-aside">
+    <a  class="btn btn-blue" href="{{ subscription.member.get_absolute_url() }}">
+      {% trans %}Go to user profile{% endtrans %}
+    </a>
+    <a  class="btn btn-grey" href="{{ url("subscription:subscription") }}">
+      {# We don't know if this fragment is displayed after creating a subscription
+      for a previously existing user or for a newly created one.
+      Thus, we don't know which form should be used to create another subscription
+      in this place.
+      Therefore, we reload the entire page. It just works. #}
+      {% trans %}Create another subscription{% endtrans %}
+    </a>
+  </div>
+</div>