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/Cargo.lock

@@ -4599,7 +4599,7 @@ dependencies = [
 
 [[package]]
 name = "pallet-contracts"
-version = "2.0.1"
+version = "3.0.0"
 dependencies = [
  "assert_matches",
  "frame-benchmarking",
@@ -4630,7 +4630,7 @@ dependencies = [
 
 [[package]]
 name = "pallet-contracts-primitives"
-version = "2.0.1"
+version = "3.0.0"
 dependencies = [
  "bitflags",
  "parity-scale-codec",
@@ -4640,7 +4640,7 @@ dependencies = [
 
 [[package]]
 name = "pallet-contracts-proc-macro"
-version = "0.1.0"
+version = "3.0.0"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -4649,7 +4649,7 @@ dependencies = [
 
 [[package]]
 name = "pallet-contracts-rpc"
-version = "0.8.1"
+version = "3.0.0"
 dependencies = [
  "jsonrpc-core",
  "jsonrpc-core-client",
@@ -4668,7 +4668,7 @@ dependencies = [
 
 [[package]]
 name = "pallet-contracts-rpc-runtime-api"
-version = "0.8.1"
+version = "3.0.0"
 dependencies = [
  "pallet-contracts-primitives",
  "parity-scale-codec",