Add `AirdropSupply` option

[lubtd]

Most of the time, the total amount to be distributed for airdrop will not be calculated dynamically from the sum of all claim records obtained from the snapshots and formula, but each claim record will be calculated from a fixed airdrop supply

airdrop.yml:

AirdropSupply: 1000000udrop

Invariant:

AirdropSupply == (DustWallet * NbClaimRecords) + Σ(ClaimRecord)

There should be an additional step in the claim records creation that calculate the final claim record from the processed data and airdrop supply:

(naming not definitive, just ideas)

- [BlockchainState]

-> snapshot()

- [RawSnapshotData]

-> filter(addresses)

- [FilteredSnapshotData]

-> process(formula)

- [ProcessedSnapshotData]

-> finalize(airdropSupply)

- [ClaimRecords] + [WalletBalances] (dust wallets)