Fixed a couple migrate:rollback issues

[marcusmoore]

Description

This small PR fixes two issues in the down methods for migrations:

• created_by wasn't being reverted properly
• There was an attempt to use varchar when it should be string

I personally rarely use migrate:rollback but allowing it to complete successfully it is 👍🏾

Type of change

• Bug fix (non-breaking change which fixes an issue)

[what-the-diff]

PR Summary

• Modification of Data Type in System Setting
  We adjusted the nature of the webhook_endpoint variable in the system's settings. It was initially set to a varchar type (vaguely equivalent to lines of text), but we've updated it to a string type, which is a simpler, more flexible form of representing text and numbers.

• Alteration in Column Name in User Information
  In the part of the system where users' information is maintained, we have renamed an important attribute. Previously known as user_id, it is now termed created_by. This change reflects a shift in how we intend to reference and utilize this specific attribute.