Suggest using numeric whodunnit column type for performance

[fatkodima]

We are currently using paper_trail and have billions of items in the versions table and the table is huge.
One of the easy improvements that could have been done back then was using numeric type for whodunnit column. We currently plan to switch to integer which is 4 bytes, while using strings to store integer values can easily require much more space, like for 1000000 it will require 8 bytes (padding included), so twice the space. And also integers have statis types, which is easier for databases to work with.

So, I think it is a good idea at least to suggest people to consider switching to numeric types in the migration's comment.

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[fatkodima]

Ping.