Clean up `vibotChannels.js`

Current Behaviour

Problems, Frustrations, General Description

commands/vibotChannels.js has a lot of code that are related to other commands. The code is also very messy and could use some spring cleaning.

Wanted/Expected Behaviour

Improvements, Additions, Changes

Preferably, all functions, listeners, etc. should be moved into their respective modules & then imported into vibotChannels. #701 removes the use & need of updateModmailListeners and we'd like to hopefully remove the need for this file entirely, if possible.

Tasks

Things to Do

• updateRoleAssignmentListeners - move to commands/roleAssignment.js and refactor code
• find out if any of the remaining code is needed and refactor or remove as needed, I am inclined to believe the only functional aspect here is updateRoleAssignmentListeners

Paths to Files

• commands/vibotChannels.js
• commands/roleAssignment.js