getPostOnRampQuote
When buying a token with fiat currency - It only involes doing on-ramp if the on-ramp provider supports buying the given destination token directly.
If the on-ramp provider does not support buying the destination token directly, user can be sent an intermediate token with fiat currency from the on-ramp provider which can be swapped to destination token onchain.
getPostOnRampQuote  function is used to get the quote for swapping the on-ramp token to destination token.
 When you get a "Buy with Fiat" status of type "CRYPTO_SWAP_REQUIRED" from the getBuyWithFiatStatus  function,
you can use getPostOnRampQuote  function to get the quote of type BuyWithCryptoQuote  for swapping the on-ramp token to destination token
 Once you have the quote, you can start the Swap process by following the same steps as mentioned in the getBuyWithCryptoQuote  documentation.
 Object of type BuyWithCryptoQuote  which contains the information about the quote such as processing fees, estimated time, converted token amounts, etc.