Group level code owners
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### Proposal
[Code owners](https://docs.gitlab.com/ee/user/project/code_owners.html) is currently only supported at the project level. This request is to enable code owners at the group level.
The typical use case is that a business unit (BU), which maps to a top level group in GitLab, will need to set up code owner rules for all their projects. For example, all .gitlab-ci.yaml files must be reviewed by the BU’s CICD champions team.
Customer request: https://gitlab.my.salesforce.com/00161000004zrG3
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