Total Quantity in Sales and Purchase DocTypes (#14114)

* Add  field to all sales and purchase doctypes

* Add patch to update existing records

* Modify taxes_and_totals.py
diff --git a/erpnext/controllers/taxes_and_totals.py b/erpnext/controllers/taxes_and_totals.py
index d1c42b8..d1a75a9 100644
--- a/erpnext/controllers/taxes_and_totals.py
+++ b/erpnext/controllers/taxes_and_totals.py
@@ -164,9 +164,10 @@
 			return tax.rate
 
 	def calculate_net_total(self):
-		self.doc.total = self.doc.base_total = self.doc.net_total = self.doc.base_net_total = 0.0
+		self.doc.total_qty = self.doc.total = self.doc.base_total = self.doc.net_total = self.doc.base_net_total = 0.0
 		for item in self.doc.get("items"):
 			self.doc.total += item.amount
+			self.doc.total_qty += item.qty
 			self.doc.base_total += item.base_amount
 			self.doc.net_total += item.net_amount
 			self.doc.base_net_total += item.base_net_amount