Add display of current assigned role users to the assignable role place

[Sheldan]

General Information

• I have checked for similar issues on the Issue-tracker.
• I have updated to the latest version
• I have checked the branches or the maintainers' PRs for upcoming features fixes.

Description

Add the current amount of users which are known to the bot to the assignable role, to mimic the old functionality of reactions, where you were able to tell how many users had a certain role from just the message.

Feature worth and general use

Some people prefer to know how many people have a certain role without them having access to moderation tools. People would be able to see it that way.

Suggestions for implementation

When setting up the assignable role it should load the current users with this role with an initial value.
Each time a role is added or removed increment/decrement this counter.
The display can either be part of the button or in the embed.