Return babe configuration information in the babe api epoch functions (#8072)

* Make changes

* Add serialize/deserialize, copy babe epoch config defaults from node runtime

* Fix line widths and turn default features off for serde

* Remove ser/deser from Epoch, fix node-cli

* Apply suggestions

* Add comment to BABE_GENESIS_EPOCH_CONFIG in bin

* Apply suggestions

* Add a sketchy migration function

* Add a migration test

* Check for PendingEpochConfigChange as well

* Make epoch_config in node-cli

* Move updating EpochConfig out of the if

* Fix executor tests

* Calculate weight for add_epoch_configurations

* Fix babe test

* Apply suggestions from code review

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Add more asserts to tests, remove unused changes to primitives/slots

* Allow setting the migration pallet prefix

* Rename to BabePalletPrefix

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

substrate/bin/node/testing/src/genesis.rs

@@ -23,7 +23,7 @@ use sp_keyring::{Ed25519Keyring, Sr25519Keyring};
 use node_runtime::{
 	GenesisConfig, BalancesConfig, SessionConfig, StakingConfig, SystemConfig,
 	GrandpaConfig, IndicesConfig, ContractsConfig, SocietyConfig, wasm_binary_unwrap,
-	AccountId, StakerStatus,
+	AccountId, StakerStatus, BabeConfig, BABE_GENESIS_EPOCH_CONFIG,
 };
 use node_runtime::constants::currency::*;
 use sp_core::ChangesTrieConfiguration;
@@ -100,7 +100,10 @@ pub fn config_endowed(
 		pallet_contracts: ContractsConfig {
 			current_schedule: Default::default(),
 		},
-		pallet_babe: Default::default(),
+		pallet_babe: BabeConfig {
+			authorities: vec![],
+			epoch_config: Some(BABE_GENESIS_EPOCH_CONFIG),
+		},
 		pallet_grandpa: GrandpaConfig {
 			authorities: vec![],
 		},