Retroactive Experience for LevelUp

[ZooFology]

Introduction:
After 5 years of hosting my discord server, I have recently began using levelUp as our FIRST leveling system. I believe it would be beneficial for users' levels to reflect the time they joined the server.

Feature Request:
I propose the addition of a retroactive experience feature to the LevelUp Cog. This feature would check the join date of each user, calculate the time that has passed since their join date, and grant them a relevant amount of XP based on the elapsed time.

To determine the amount of experience to be given, the bot could use a formula where the time is multiplied by the XP value. Additionally, it would be useful to allow the configuration of the time unit between days, weeks, and months.

Possible Issues:
One concern is the potential optimization challenge if the bot attempts to update all users at once. As an alternative solution, I propose implementing the feature with the following commands:

Method 1:
Command: [p]levelset retro <timeunit> <xp> <messageID>

This method involves creating a reaction on a specified message. When a user reacts to the message, they will be granted their retroactive XP.

Method 2:
Command: [p]levelset retro <timeunit> <xp> <RoleID>

In this method, users would gain their retroactive experience when they are granted a specific role. This approach could be useful if you want users to introduce themselves or meet certain criteria before being granted retroactive experience.

Thank you for considering this feature request. I believe that implementing retroactive experience will enhance your leveling system and provide a more accurate representation of users' longevity with the server.