Following the passing vote of the [Interim Treasury Program Referendum](https://moonriver.polkassembly.network/referendum/121), we propose to add the 5 members to the Treasury Council. 

Here is the link to the Community Forum Discussion [post](https://forum.moonbeam.foundation/t/referendum-121-status-passed-moonriver-treasury-proposal/183/5)

Set the collective's membership.

- `new_members`: The new member list. Be nice to the chain and provide it sorted.
- `prime`: The prime member whose vote sets the default.
- `old_count`: The upper bound for the previous number of members in storage. Used for
  weight estimation.

Requires root origin.

NOTE: Does not enforce the expected `MaxMembers` limit on the amount of members, but
      the weight estimations rely on it to estimate dispatchable weight.

# WARNING:

The `pallet-collective` can also be managed by logic outside of the pallet through the
implementation of the trait [`ChangeMembers`].
Any call to `set_members` must be careful that the member set doesn't get out of sync
with other logic managing the member set.

# <weight>
## Weight
- `O(MP + N)` where:
  - `M` old-members-count (code- and governance-bounded)
  - `N` new-members-count (code- and governance-bounded)
  - `P` proposals-count (code-bounded)
- DB:
  - 1 storage mutation (codec `O(M)` read, `O(N)` write) for reading and writing the
    members
  - 1 storage read (codec `O(P)`) for reading the proposals
  - `P` storage mutations (codec `O(M)`) for updating the votes for each proposal
  - 1 storage write (codec `O(1)`) for deleting the old `prime` and setting the new one
# </weight>

- The Interim Treasury Program Referendum passed.
- 5 members will be added to the Treasury Council.
- There is a link to a post with more information.
- The post is on the Community Forum Discussion.
- The post discusses the status of the referendum.

#124 Interim Treasury Program member registration