Created entrypoint for migrations

samples/MicroserviceDemo/databases/entrypoint.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+cd /src/ProductService.Host
+
+until dotnet ef database update --no-build; do
+>&2 echo "SQL Server is starting up"
+sleep 1
+done
+
+cd /src/AuthServer.Host && dotnet ef database update --no-build