Roletools: Allow for more options for the cost of acquiring a role

[ElderCub]

We would like our users to self balance a variety of roles, or "teams" they're on.

Primary feature request: To do this we've come up with the idea of increasing the cost of a role based on how many users already have it, an example formula would be 'Base cost + (2.5 x Role Number)' or displayed more accurately to what we would enter through the command '100+(2.5x@562302465253441537)'

Secondary request: After this a message would appear stating who paid how much for the role, or a message stating they couldn't afford the role, the message would be deleted after an amount of time (possibly configurable)

It would be nice if the bot could manage the message housing the react roles and live update the cost of each role, but that sounds like much more work to add

Additional context We've considered cooldowns, but no cog appears to do that for react roles and the difference in price will help towards balancing the roles