Allow arbitrary number of SignalR standard units to be purchased
Currently Azure customers can only select from a predefined quantity of standard units for the monthly purchase. Those options are 1, 2, 5, 10, 20, 50, ... This is unnecessarily costly to customers when customers have a stable number of concurrent connections is known to be expected month over month, but which doesn't align with the predefined unit quantities. Customers should be able to enter any arbitrary number into the quantity field.