Added a new table ‘stats_template_usage_by_month’

Currently the 'See templates used by month' report is timing out for
some services due to the query time of the data from notification_history
This is a stats table which will hold the data and will be updated by a
scheduled celery task once a day. This data will be combined with the
'live' data from notifications tables (which will be considerably less)
to form the data of the new report.

app/models.py

@@ -1555,3 +1555,37 @@ class AuthType(db.Model):
     __tablename__ = 'auth_type'
 
     name = db.Column(db.String, primary_key=True)
+
+
+class StatsTemplateUsageByMonth(db.Model):
+    __tablename__ = "stats_template_usage_by_month"
+
+    template_id = db.Column(
+        UUID(as_uuid=True),
+        db.ForeignKey('templates.id'),
+        unique=False,
+        index=True,
+        nullable=False,
+        primary_key=True
+    )
+    month = db.Column(
+        db.Integer,
+        nullable=False,
+        index=True,
+        unique=False,
+        primary_key=True,
+        default=datetime.datetime.month
+    )
+    year = db.Column(
+        db.Integer,
+        nullable=False,
+        index=True,
+        unique=False,
+        primary_key=True,
+        default=datetime.datetime.year
+    )
+    count = db.Column(
+        db.Integer,
+        nullable=False,
+        default=0
+    )