meta: introduce codeowners again

The Contributor's Survey results highlight the fact that it is often not easy for contributors to know who the right people are to talk to about a proposed change or who to ask for reviews of a given subsystem. We briefly toyed around with codeowners before when GitHub introduced it but just as quickly disabled it because the structure of our repository made it exceedingly difficult to get right.

Rather than start with a codeowners for the entire project, I propose that we start with a small experiment focused on specific subsystems. Specifically, codeowners for modules, streams, net/tls, http/http2, and quic (once that lands). We can expand out from there as we see how things go with the minimal starter set.

A couple of points:

1. A codeowner should always be a team, never an individual person
2. Each codeowner team should contain at least one TSC member (to provide coverage for signing off on semver-major changes)
3. PRs touching any code with a codeowner must be signed off by at least one person on the codeowner team

/cc @nodejs/tsc

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines