contracts: Release as v3.0.0 and add reserved field to ContractInfoOf (#8175)

* contracts: Update README

* contracts: Add CHANGELOG.md

* contracts: Bump version to v3.0.0 and allow publish

* Typos

Co-authored-by: Andrew Jones <ascjones@gmail.com>

* Improve wording in the changelog

* contracts: Add reserved field to ContractInfoOf for future proofing

* also bump frame-benchmarking

* update lockfile

Co-authored-by: Andrew Jones <ascjones@gmail.com>
Co-authored-by: Benjamin Kampmann <ben@parity.io>

substrate/frame/contracts/src/storage.rs

@@ -182,6 +182,7 @@ where
 				rent_payed: <BalanceOf<T>>::zero(),
 				pair_count: 0,
 				last_write: None,
+				_reserved: None,
 			};
 
 			*existing = Some(contract.into());