Add withdrawal API to Gateway SDK

[gregdhill]

For strategies we support it should be possible to wrap the full withdrawal process e.g. SolvBTC.BBN -> SolvBTC -> wBTC -> BTC.

[gregdhill]

This is especially useful if the user bridges e.g. xSolvBTC via CCIP to our chain and we want to withdraw in the same step.

[nakul1010]

The code should not be restricted to only solvBTC/ionBTC or the strategy's output token. Users should also be able to convert, for example, 100 USDC to BTC via an OKU swap behind the scenes. Therefore, supporting arbitrary call data would make more sense.