soroban-rpc : add support for fee calculations

[tsachiherman]

What ?

The rs-soroban-env now contains library functions to calculate the fees needed by a transaction, based on it's resources.
Our goal is to integrate that into simulateTransaction endpoint in soroban-rpc. This issue is about the second step in the process:
We need to use the exposed fee calculation method we previously created in #622, and use it during simulateTransaction in order to calculate the suggested fees. Then, we need to modify the returned json to include the following:
( all the TransactionResources fields, that you've already used when calling compute_transaction_resource_fee )

• Number of instructions
• Number of reads
• Number of writes
• Read bytes count
• Write bytes count
• Metadata size
• Transaction size
  ( plus )
• Fee ( Minimal inclusion fee )
• RefundableFee

Epic

• [epic] Platform May Release  #519

Dependencies

• soroban-rpc: update xdr #627
• soroban-rpc: Fix integration tests #628

[2opremio]

I think this is fully addressed in #636

[tsachiherman]

I think this is fully addressed in #636

Just close both when you're done with 636, as this one was supposed to be the go side and the other on the preflightlib side.