Group Code Owner rules with matching patterns and sections
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When a file pattern is repeated within a section, group the owners together instead of using the "last rule wins" approach. For example
```
[Documentation]
README.md @test
[DocuMentatION]
README.md @delicia
```
Currently, this gives us
```
Documentation
README.md @delicia
```
..but should result in
```
Documentation
README.md @test @delicia
```
(h/t to @m_gill for this example: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36383#note_376571396)
Additionally, this would be a good Code Owners Linter/Verification item to flag as a :yellow_heart:
issue