Refactor SwapService interface to allow cross-chain swaps

[onyb]

We want generic methods in SwapService to query swap/bridge quotes without relying on the underlying provider (0x, Jupiter, etc).

Here's an example of the methods that we can have:

GetQuote(SwapQuoteParams params) =>
      (SwapQuoteUnion? response, SwapErrorUnion? error, string error_string);

  GetTransaction(SwapTransactionParamsUnion params) =>
      (SwapTransactionUnion? response, SwapErrorUnion? error, string error_string);