Create Rates resource + migration

[sl0wik]

Create rates resource (migration + updated model) with new rate schema available here https://whimsical.com/booking-VrUF3bVpqu7JEjKy9tmr3Q.

Add rate categories that used for grouping rates.

Add command to migrate existing schema to a new schema (methodology: whatever works, perhaps could generate inserts from old structure? Will be executed once).

[drewroberts]

The command doesn't need to be added to the package. We'll just do that on the existing project repo.

[drewroberts]

New rate schema ... https://whimsical.com/booking-VrUF3bVpqu7JEjKy9tmr3Q

This looks good. I like this approach. Thank you, @sl0wik!