Support third party withdrawals with queueWithdrawalsWithSignature

[peitalin]

Description
Support third party withdrawals by adding a queueWithdrawalWithSignature function in DelegationManager so that a contract can queue withdrawals on behalf of a user with their signature.

Use Cases
At the moment a contract (e.g. a contract facilitating L2 <-> L1 restaking and withdrawing) can conduct deposits on behalf of a staker with depositIntoStrategyWithSignature in the StrategyManager, but can't queue withdrawals on behalf of a staker. Adding this feature would enable withdrawing via L2.

The token which we are using for Dual Staking has most of it's liquidity and users on L2, and so we wanted to allow our users to both stake and withdraw from Eigenlayer from L2 instead of: requiring our users to bridge ETH back to L1, queueWithdrawal from Eigenlayer, waiting for the withdrawal period, completeWithdrawal, then bridging back to L2.

Update:
The Eigenlayer team mentioned this feature existed in the past but was removed due to phishing concerns.
I'm wondering if adding a whitelistThirdPartyWithdrawer(contractAddr, strategy) with checks in the queueWithdrawalWithSignature function addresses these concerns sufficiently.

At the moment, queueWithdrawals already checks if thirdPartyTransfersForbidden = false to allow third party withdrawals, however thirdPartyTransfersForbidden defaults to false in StrategyFactory.deployNewStrategy(), so I'm unsure if the team wants to add a separate thirdPartyWithdrawalsForbidden = false requirement to allow for different defaults for third party deposits, and third party withdrawals.

Happy to add a separate thirdPartyWithdrawalsForbidden feature in the PR as well if the team prefers the latter.

[peitalin]

Edit: Seems like this feature puts the DelegationManager contract size just above the size limit:

| Contract                    | Size (B) | Margin (B) |
|-----------------------------|----------|------------|
| DelegationManager           |   25,019 |       -443 |

However if we turn require() error messages into custom errors as in this branch we see:

| Contract                    | Size (B) | Margin (B) |
|-----------------------------|----------|------------|
| DelegationManager           |   23,576 |        1000 |