Implement a new Merkle campaign with variable claim amount

[smol-ninja]

As discussed in https://github.com/sablier-labs/company-discussions/discussions/85, implement a new merkle contract with the following features:

• The amount of airdropped token depends on the claim timestamp.
• Only works for ranged streams i.e. all streams begin at the same time.
• Enforce expiry to be greater than end time of the vesting schedule.
• Nomenclatures TBD.

function createMerkleVCA(
    MerkleBase.ConstructorParams memory baseParams,
    MerkleLL.Schedule memory schedule,
    uint256 aggregateAmount,
    uint256 recipientCount
)

Calculation of airdropped amount

$$\text{airdrop amount} = \text{claim amount} \cdot \frac{\text{block timestamp} - \text{start time}}{\text{total duration}}$$

Some questions

1. Should it have start and cliff unlocks?
2. What should the contract be called?