Warehouses page enhancements

We've made several enhancements to the warehouses page to help users explore warehouse costs and performance, and identify opportunities to consolidate warehouses:

1. Chart added above the warehouses table. Users can filter to a subset of warehouses and plot a variety of different metrics: Spend, Automated Savings, Query Counts and Utilization Efficiency.
2. Utilization Efficiency has been added as a column to the warehouses table. Users can leverage this to identify warehouses which should be combined to improve their utilization.