RPC endpoint for fee calculation

Currently tezos-client performs baker fee calculation based on a formula defined in this doc.

However, it's quite nontrivial to calculate proper baker fee when submitting operations to the node using plain RPC requests without calling tezos-client.

AFAIU, fee constants are defined for each tezos-node individually, so it would be nice to have a way to calculate a fee for a given operation using a dedicated RPC endpoint similar to run_operation.