Follow-up from "Do not try to copy weight events when promoting an issue"

Issue weights is a EES feature, still ResourceWeightEvents model is in core and some of the related code.

We should cleanup the code and move it to the appropriate structure.

The following discussion from !43891 (merged) should be addressed:

• @.luke started a discussion: (+1 comment)

  Thought (non-blocking)

  🤔 It looks like issues only have resource_weight_events in EE. It makes me wonder if the #copy_resource_weight_events method should technically be in an EE module? The ResourceWeightEvent model is in Core, but it looks like all other code besides this method that uses it is in EE? Even if the answers are yes, this can totally be non-blocking as this is a priority1 fix; any of this could be a follow-up MR if needed.