Implement `CommitteeBLSATMSPolicy`

## Description

Based on the implementation of input-output-hk/trustless-sidechain#44, we should provide a way to use BLS signature scheme as a modular committee verification option.
This might also need some research.

## Blocked by

- native support for BLS pairing in PlutusTx

## Related issues/PRs

input-output-hk/trustless-sidechain#44