All developers are reviewers

This includes a few changes (probably by order of importance):

1. 9dde67dc1 From the responsibilities listed at https://about.gitlab.com/positions/developer/#responsibilities, it's in every developers responsibilities to "manage and review" MRs from the community. I've added an item to state that they should also review MRs from their coworkers.
2. dde760a36 Remove obvious items from the MR coach responsibilities. Ideally, I don't think we should have a special role for developers to handle community MRs in the future: it's all developers' responsibility & job.
3. 72467fbc3 I've improved the Engineering root page:

• New paragraph for code quality and standards linking to our documentation (SSOT)
• New paragraph for code reviews linking to our documentation (SSOT)
• Remove "working in teams" from the root page since it's already covered in the workflow page

1. d5894558f Use the "developer responsibilities" partial in all the developer job pages