Include ability to specify desired free space in cool access cost calculator

https://azure.github.io/azure-netapp-files/coolaccess-calc/

The calculator allows you to model the possible savings if you enable cool access for an existing workload. All amounts are based on a utilization of 100% with no mention of unallocated or free space. Because of this, the current and projected costs are not what you will actually be charged by the service.

For example, if If using the default settings on page load and we want to account for 25% free space we'd need to add (500 * (1/.75) = 166 TiB of hot tier costs for every cost summary, and a lower (but more accurate) monthly savings % on overall service costs.

Can an input for free space be added to the calculator?

Open the calculator at https://azure.github.io/azure-netapp-files/coolaccess-calc/ and inspect how its inputs and cost summaries are presented. Add a free-space input that affects the current and projected costs and monthly savings percentage; done means the default calculation and a 25% free-space scenario reflect the stated utilization adjustment.

Written by the indexing model from the issue text.