Benchmark Staking and Session Pallet (#5183)

* starting bench

* More

* more

* Payout Validator

* Give each validator exactly n nominators

* Update with test

* Try to add accounts to chain spec

* Undo changes to chainspec

* Payout nominator

* Rebond and Reap Stash

* Set history depth

* fix smelly code

* cancel deferred slash

* new_era bench

* do_slash benchmark

* Add features

* undo extrinsic move

* lower

* Update new era

* Update benchmarking.rs

* whitespace

* Apply suggestions from code review

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* fixes

* nit

* Refactor tests, initial code

* Move session benchmarks to avoid cyclic deps

* Update lib.rs

* Fix warnings

* Move impl

* Update to do random nominator allocation

* add feature to benchmark pallet

* Remove extra stuff

* Update based on feedback

* Less intrusive

* Remove `transfer_idle_users`

* remove again

* unused dep

* test feature flag

* Update to latest substrate

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

substrate/Cargo.lock

@@ -3543,6 +3543,7 @@ dependencies = [
  "pallet-randomness-collective-flip",
  "pallet-recovery",
  "pallet-session",
+ "pallet-session-benchmarking",
  "pallet-society",
  "pallet-staking",
  "pallet-staking-reward-curve",
@@ -4396,6 +4397,18 @@ dependencies = [
  "sp-trie",
 ]
 
+[[package]]
+name = "pallet-session-benchmarking"
+version = "2.0.0-alpha.3"
+dependencies = [
+ "frame-benchmarking",
+ "frame-system",
+ "pallet-session",
+ "pallet-staking",
+ "sp-runtime",
+ "sp-std",
+]
+
 [[package]]
 name = "pallet-society"
 version = "2.0.0-alpha.3"
@@ -4416,6 +4429,7 @@ dependencies = [
 name = "pallet-staking"
 version = "2.0.0-alpha.3"
 dependencies = [
+ "frame-benchmarking",
  "frame-support",
  "frame-system",
  "pallet-authorship",
@@ -4424,6 +4438,7 @@ dependencies = [
  "pallet-staking-reward-curve",
  "pallet-timestamp",
  "parity-scale-codec",
+ "rand_chacha 0.2.1",
  "serde",
  "sp-core",
  "sp-io",