Closes #5858: Implement a quick-add UI widget for related objects (#18016)

* WIP

* Misc cleanup

* Add warning re: nested quick-adds

netbox/templates/htmx/quick_add.html

@@ -0,0 +1,28 @@
+{% load form_helpers %}
+{% load helpers %}
+{% load i18n %}
+
+<div class="modal-header">
+  <h2 class="modal-title">
+    {% trans "Quick Add" %} {{ model|meta:"verbose_name"|bettertitle }}
+  </h2>
+  <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
+</div>
+<div class="modal-body row">
+  <form
+      hx-post="{% url model|viewname:"add" %}?_quickadd=True&target={{ request.GET.target }}"
+      hx-target="#htmx-modal-content"
+      enctype="multipart/form-data"
+  >
+    {% csrf_token %}
+    {% include 'htmx/form.html' %}
+    <div class="text-end">
+      <button type="button" class="btn btn-outline-secondary btn-float" data-bs-dismiss="modal" aria-label="Cancel">
+        {% trans "Cancel" %}
+      </button>
+      <button type="submit" name="_quickadd" class="btn btn-primary">
+        {% trans "Create" %}
+      </button>
+    </div>
+  </form>
+</div>

netbox/templates/htmx/quick_add_created.html

@@ -0,0 +1,22 @@
+{% load form_helpers %}
+{% load helpers %}
+{% load i18n %}
+
+<div class="modal-header">
+  <h2 class="modal-title">
+    {{ object|meta:"verbose_name"|bettertitle }} {% trans "Created" %}
+  </h2>
+  <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
+</div>
+<div class="modal-body row">
+  {# This content is intended to be scraped and populated in the targeted selection field. #}
+  <p id="quick-add-object"
+      data-object-repr="{{ object }}"
+      data-object-id="{{ object.pk }}"
+      data-target-id="{{ request.GET.target }}"
+  >
+    {% blocktrans with object=object|linkify object_type=object|meta:"verbose_name" %}
+      Created {{ object_type }} {{ object }}
+    {% endblocktrans %}
+  </p>
+</div>