Extract fee-structure crate

[kevinheavey]

Problem

solana_sdk::fee imposes a solana_sdk dependency on solana_svm and solana_compute_budget

Summary of Changes

• Move to its own crate and re-export with deprecation in solana_sdk. I've named the new crate solana-fee-structure based on the top level doc comment for fee.rs. solana-fee is already taken.
• Make serde optional in the new crate
• Add doc_auto_cfg