Restructure the Code Owner role

[ahoppen]

The description of the Code Owner role no longer fitted the reality and did not match the pattern of the Member and Code Merger role. Update it to reflect the reality of maintaining a .github/CODEOWNERS file and match the structure of the other two roles.

[parispittman]

Commenting on the location of this and not the content -
I think it's time we move this to /project-operations as contributor-ladder.md in the root and then call that from the guide as a canonical link. We've been having convos about how to make the guide more basic for all, less scroll worthy, and then niche items are inside of the /project-operations repo.
Website Workgroup folks - I know I've discussed this with a few of you as well - what do you think?