pallet-broker: redesign bulk coretime market according to the rfc-17

[mertwole]

RFC-17 proposes bulk coretime market redesign. The key changes as proposed in RFC-17 include:

• Reverse the order of the market and renewal phases: all cores are first offered on the open market, and only then are renewal options made available.
• Introduce a dynamic reserve_price, which is the minimum price coretime can be sold for in a period. This price adjusts based on consumption and does not rely on market participation.
• Make unproductive core captures sufficiently expensive, as all cores are exposed to the market price.

Implementation can be split into the following stages:

• Decouple the current coretime auction logic from the pallet, exposing a generic interface in the pallet config.
• Implement the auction logic according to RFC-17.