[P4] [MCP/Codeowners] Edit CODEOWNERS file

Read CODEOWNERS file into objects
Insert/update entries
Serialize output into CODEOWNERS file so PR only shows the lines added (i.e. other lines of the file are not disturbed)

❓ Open questions
* How do we handle project dependencies (e.g. CodeownersParser)

Start by locating the CODEOWNERS handling entry point in the repository and read how the file is currently accessed. Define how entries should be read into objects, inserted or updated, and serialized without disturbing unrelated lines. Resolve the open question about using a project dependency such as CodeownersParser before implementation.

Written by the indexing model from the issue text.