accept payload instead of executeData in estimateGasFee query

[canhtrinh]

Is your feature request related to a problem? Please describe.
payload is the encoded function call on the source chain. executeData is the GMP transaction that arrives on the destination chain that includes: commandId, sourceChain, sourceAddress, payload`.

Describe the solution you'd like
We should not have to necessarily expect users to be able to calculate executeData from their known payload. We should accept payload and calculate the executeData for them.