Add feature to assign role based on reaction to a post

[morcup]

My feature request is about

• A new feature
  I would like to see a way to add roles to users when they react to a post.

Description of the solution I'd like
The bot will assign a role based on which reaction they add to a certain post

Alternatives I've considered
Manually assigning roles

Additional context
none

What needs to be done

• Implement role attribution through reaction
• Document it in the #Role section

[s0lst1ce]

For now this will only be implemented with the event planner command.