pallet-membership should implement ContainsLengthBound (#4865)

### ISSUE
Link to the issue:
#1143

Deliverables
 - Implement trait `ContainsLengthBound` for pallet-membership
 

### Test Outcomes
___
Successful tests by running `cargo test -p pallet-membership --features
runtime-benchmarks`



running 22 tests
test tests::__construct_runtime_integrity_test::runtime_integrity_tests
... ok
test benchmark::bench_clear_prime ... ok
test tests::add_member_works ... ok
test tests::change_key_with_same_caller_as_argument_changes_nothing ...
ok
test tests::change_key_works ... ok
test benchmark::bench_set_prime ... ok
test benchmark::bench_remove_member ... ok
test benchmark::bench_change_key ... ok
test tests::change_key_works_that_does_not_change_order ... ok
test benchmark::bench_reset_members ... ok
test benchmark::bench_add_member ... ok
test tests::genesis_build_panics_with_duplicate_members - should panic
... ok
test benchmark::bench_swap_member ... ok
test tests::query_membership_works ... ok
test tests::prime_member_works ... ok
test tests::test_genesis_config_builds ... ok
test tests::remove_member_works ... ok
test tests::migration_v4 ... ok
test tests::swap_member_with_identical_arguments_changes_nothing ... ok
test tests::swap_member_works_that_does_not_change_order ... ok
test tests::swap_member_works ... ok
test tests::reset_members_works ... ok

test result: ok. 22 passed; 0 failed; 0 ignored; 0 measured; 0 filtered
out; finished in 0.01s

   Doc-tests pallet_membership

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered
out; finished in 0.00s

---------

Co-authored-by: Bastian Köcher <[email protected]>

prdoc/pr_4865.prdoc

@@ -0,0 +1,13 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Implement trait `ContainsLengthBound` for pallet-membership
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Implement trait ContainsLengthBound for pallet membership otherwise we can't use it with pallet-tips without wrapper
+
+crates:
+  - name: pallet-membership
+    bump: minor

substrate/frame/membership/src/lib.rs

@@ -24,7 +24,7 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use frame_support::{
-	traits::{ChangeMembers, Contains, Get, InitializeMembers, SortedMembers},
+	traits::{ChangeMembers, Contains, ContainsLengthBound, Get, InitializeMembers, SortedMembers},
 	BoundedVec,
 };
 use sp_runtime::traits::{StaticLookup, UniqueSaturatedInto};
@@ -361,6 +361,17 @@ impl<T: Config<I>, I: 'static> Contains<T::AccountId> for Pallet<T, I> {
 	}
 }
 
+impl<T: Config> ContainsLengthBound for Pallet<T> {
+	fn min_len() -> usize {
+		0
+	}
+
+	/// Implementation uses a parameter type so calling is cost-free.
+	fn max_len() -> usize {
+		T::MaxMembers::get() as usize
+	}
+}
+
 impl<T: Config<I>, I: 'static> SortedMembers<T::AccountId> for Pallet<T, I> {
 	fn sorted_members() -> Vec<T::AccountId> {
 		Self::members().to_vec()