Support account-level custom price granularity

[bretg]

Currently account-level price granularity doesn't support the 'custom' value. Custom price buckets must be defined in the request or storedrequest.

This issue tracks the expansion of account-level custom price granularity buckets. We propose re-using the existing price-granularity config, but allowing either a string datatype for the existing behavior, or an object for the new behavior.

Example account-level config:

auction.price-granularity.type: "custom"
auction.price-granularity.precision: 2
auction.price-granularity.ranges: [{"max": 20.00, "increment": 0.10},{"max": 50.00, "increment": 1.00}]

Priority of granularity config:

• request
• stored request
• account config