Election of ValidatorSet based on VRF

[torao]

This is a story ticket to modify the ValidatorSet election performed on the Cosmos side to a VRF-based method. Before making any modification, it should investigate whether it's able to change the algorithm for the ValidatorSet selection.

1. Whether should we release ValidatorSet selections in the VRF together with Proposer (at the beginning of the implementation, it was assumed that the selection of ValidatorSet is left to Cosmos and Proposer is selected from among them).
2. Find out where ValidatorSet elections are taking place in Cosmos and confirm whether the VRF hash contained in the block can be referenced.
3. Implement if possible. (TBC)