[MR Widget] Add Engineering DRIs as CODEOWNERs

Proposal

In the context of the WorkingGroupMergeRequestReportWidgets, we have devised a list of DRIs for the engineering of each widgets.

With the Working Group approaching it's extinction, it's important to start thinking about life after the working group.

In a recent discussion, it came up the idea of adding each DRI as CODEOWNER for each of their widgets.

That would crystalize their ownership in code rather than simply in documentation.