Add task that requests funds from the shadowfork vault

[pk910]

Add a task that requests funds from the shadowvault

The shadowfork vault is a contract deployed to public testnets that is designed to release funds safely on a shadow fork.
Withdrawal transactions to this contract revert on the regular public testnets.
The contract can be used to gather some funds for subsequent tests on shadow forks.

• Add task generate_shadowvault_withdrawal
• Task should request funds from the ShadowForkVault via the shadowWithdraw function
• The required proof for the shadowWithdraw function can be generated via the generateHeaderProof function