SlackBridge don't work with modern Slack API token policy

Description:

The current Slack App does not allow token to be included in the query string parameter. Because of this, all queries from SlackBridge to the Slack API that require token will fail and SlackBridge not work properly.

Steps to reproduce:

1. Setup classic Slack app
2. Set up "Bot User OAuth Token" to SlackBridge
3. add bot to rooms in Slack
4. send some text in that room

Expected behavior:

• A room with the same name as slack will be created in RC and the text will be displayed.
• Users who join the room will be registered in the RC.

Actual behavior:

Nothing is happening

Server Setup Information:

• Version of Rocket.Chat Server: 3.17.1
• Operating System: Ubuntu 20.04
• Deployment Method: docker
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version:

Additional context

https://api.slack.com/changelog/2020-11-no-more-tokens-in-querystrings-for-newly-created-apps

Relevant logs:

Start by locating the SlackBridge implementation and the calls it makes to the Slack API. Reproduce the setup with a classic Slack app and Bot User OAuth Token, then trace the failing requests under Slack's no-query-string-token policy. Done means rooms and users are synchronized and messages appear in Rocket.Chat.