[Federation] Channels cannot be federated error when add federated user to public channel

Description:

I see error in logs Channels cannot be federated when add federated user to public channel despite green popup message that adding successful
@alansikora please take a look

Steps to reproduce:

1. Search for federated user in public channel member list
2. Add federated user to public channel
3. See message that adding was successful but error in logs

Expected behavior:

Federated users should be added to public channels

Actual behavior:

Server Setup Information:

• Version of Rocket.Chat Server: 3.1.1
• Operating System: CentOS7
• Deployment Method: docker
• Number of Running Instances: 25
• DB Replicaset Oplog: Enabled
• NodeJS Version: 12.16.1
• MongoDB Version: 4.0.17

Relevant logs:

at /app/bundle/programs/server/npm/node_modules/meteor/promise/node_modules/meteor-promise/fiber_pool.js:43:40
at app/federation/server/hooks/afterAddedToRoom.js:30:10
server.js:204 Federation ➔ client.error afterAddedToRoom => Could not add user: Error: Channels cannot be federated

Start with app/federation/server/hooks/afterAddedToRoom.js and trace the after-added hook shown in the logs. Reproduce the three listed steps with a federated user and public channel, then verify that the user is added without the “Channels cannot be federated” error or a misleading success message.