bulkCreate updateOnDuplicate `createdAt` field explicitly omitted about sequelize

[LJ1102]

Looking to get feedback / approval for this bug before I put time into it.

[LJ1102]

I did some digging and found that the createdAt timestamp is explicitly removed / omitted from the updateOnDuplicate array, see:

sequelize/src/model.js

Line 2706 in 6aba382

_.without(Object.keys(model.tableAttributes), createdAtAttr),

This change was introduced with commit 0ce88c4. Initially updateOnDuplicate had a boolean option to enable all fields, in that scenario it can be assumed that we don't want to implicitly update the createdAt timestamp, however this functionality is not supported anymore, as of 8b937dd updateOnDuplicate is required to be an array of field names, in which case we can assume that if the user provides thecreatedAt field they want it to be updated, like I do, hence we can remove the exclusion of createdAt.