[Task]: Add mock request for gas estimation

### Task description

Currently, when withdrawing "stuck" funds from EVM ("layer 1.5"), Ledger users have to confirm the transaction twice;

1. to get the gas estimate for the off-ledger request
2. to confirm the actual transaction with the correct gas estimation

To improve the UX, and remove the first confirmation on ledger device, create the mock off-ledger request and fetch gas estimation and than use it in the off-ledger request in the actual transaction.
To accomplish this create `getMockLayer2WithdrawRequest` function that does similar task as the real `getLayer2WithdrawRequest` function but instead of signing the essence bytes just hardcode all 0 for the public key and the signature.