Show template usage broken down by month

This follows on from:
- https://github.com/alphagov/notifications-admin/pull/1094
- https://github.com/alphagov/notifications-admin/pull/1109

It depends on:
- [ ] https://github.com/alphagov/notifications-api/pull/829

A year is too long. Month-by-month is a better timeframe for making
decisions or seeing patterns in your usage.

app/templates/components/table.html

@@ -1,3 +1,5 @@
+{% from "components/big-number.html" import big_number %}
+
 {% macro mapping_table(caption='', field_headings=[], field_headings_visible=True, caption_visible=True) -%}
   <table class="table">
     <caption class="heading-medium table-heading{{ ' visuallyhidden' if not caption_visible}}">
@@ -129,3 +131,20 @@
     </span>
   {% endcall %}
 {% endmacro %}
+
+
+{% macro spark_bar_field(
+  count,
+  max_count
+) %}
+  {% call field(align='right') %}
+    <span class="spark-bar">
+      <span style="width: {{ count / max_count * 100 }}%">
+        {{ big_number(
+          count,
+          smallest=True
+        ) }}
+      </span>
+    </span>
+  {% endcall %}
+{% endmacro %}