Syntax highlighting for CODEOWNERS file in Blob Viewer

Problem to solve

Research justification: Help users better understand CODEOWNERS (&4498 - closed)

GitLab offers syntax highlighting for various file formats, but not for the CODEOWNERS file format.

Proposal

Enable syntax highlighting for CODEOWNERS when viewing the file in the blob viewer

Intended users

Syntax highlighting could be helpful to any GitLab user who views or edits a CODEOWNERS file.

Further details

Syntax highlighting makes source code easier to parse visually and it can also call attention to errors.