Add config for legacy that stores brackets

[ishantiw]

Description

Accept config options for legacy data to manually add range of legacy blocks for a version.

legacy: {
  brackets: [{
     startHeight: number;
     snapshotHeight: number;
     snapshotBlockID: Buffer;
  }],
  sync: boolean;
}

Add it to the application config and also update related tests

Acceptance Criteria

• Should have all the unit tests covering the above config change