Make the number of nominations configurable (#8368)

* Base features and traits.

* pallet and unsigned phase

* Undo bad formattings.

* some formatting cleanup.

* Small self-cleanup.

* Make it all build

* self-review

* Some doc tests.

* Some changes from other PR

* Fix session test

* Update Cargo.lock

* Update frame/election-provider-multi-phase/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Some review comments

* Rename + make encode/decode

* Do an assert as well, just in case.

* Fix build

* Update frame/election-provider-multi-phase/src/unsigned.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Las comment

* fix staking fuzzer.

* cargo run --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_election_provider_multi_phase --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/election-provider-multi-phase/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* Add one last layer of feasibility check as well.

* Last fixes to benchmarks

* Some more docs.

* cargo run --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_election_provider_multi_phase --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/election-provider-multi-phase/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* cargo run --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_election_provider_multi_phase --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/election-provider-multi-phase/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* Some nits

* It all works

* Some self cleanup

* Update frame/staking/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* remove most todos.

* Round of self-review.

* Fix migration

* clean macro

* Revert wrong merge

* Make the number of nominations configurable

* Self reivew

* renmae.

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Parity Benchmarking Bot <admin@parity.io>
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

substrate/bin/node/runtime/Cargo.toml

@@ -36,6 +36,7 @@ sp-keyring = { version = "3.0.0", optional = true, path = "../../../primitives/k
 sp-session = { version = "3.0.0", default-features = false, path = "../../../primitives/session" }
 sp-transaction-pool = { version = "3.0.0", default-features = false, path = "../../../primitives/transaction-pool" }
 sp-version = { version = "3.0.0", default-features = false, path = "../../../primitives/version" }
+sp-npos-elections = { version = "3.0.0", default-features = false, path = "../../../primitives/npos-elections" }
 
 # frame dependencies
 frame-executive = { version = "3.0.0", default-features = false, path = "../../../frame/executive" }
@@ -159,6 +160,7 @@ std = [
 	"pallet-vesting/std",
 	"log/std",
 	"frame-try-runtime/std",
+	"sp-npos-elections/std",
 ]
 runtime-benchmarks = [
 	"frame-benchmarking",