Add a property to `GET /reservestate` about reserve doubling info

[Cafe137]

Summary

Current reserve state:

{
  "radius": 9,
  "storageRadius": 6,
  "commitment": 20159266816
}

Desired reserve state:

{
  "radius": 9,
  "storageRadius": 6,
  "commitment": 20159266816,
  "reserveCapacityDoubling": 4
}

Motivation

• Important value to display in client tools
• Useful for optimizing stake amount in client tools

Implementation

N/A

Drawbacks

N/A