feat(backend): create template for custom admin view

backend/base_app/templates/admin/trigger_cron.html

+{% extends "admin/index.html" %} {% block content %}
+<form method="post">
+  {% csrf_token %}
+  <br />
+  <input type="submit" name="cron_name" value="update_currencies" />
+</form>
+
+<form method="post">
+  {% csrf_token %}
+  <br />
+  <input type="submit" name="cron_name" value="update_utc_ent" />
+</form>
+
+<form method="post">
+  {% csrf_token %}
+  <br />
+  <input type="submit" name="cron_name" value="update_extra_denormalization" />
+</form>
+
+<form method="post">
+  {% csrf_token %}
+  <br />
+  <input type="submit" name="cron_name" value="clear_and_clean_sessions" />
+</form>
+{% endblock %}