[MR Widget] Add Engineering DRIs as CODEOWNERs
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### Proposal
In the context of the ~"WorkingGroup::MergeRequestReportWidgets", we have devised a [list of DRIs for the engineering of each widgets](https://about.gitlab.com/handbook/engineering/development/dev/create/code-review/report-widgets-dri-list.html).
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.
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