CODEOWNERS: create initial code owners config
CODEOWNERS: create initial code owners config

In this commit, we create the initial CODEOWNERS file for `lnd`. This
file is a new-ish feature of Github that allows the maintains of a
project to define the individuals who are deemed to be experts of a
particular section of the codebase. Automated review assignment systems
can then use this file to generate required reviewers for a section of
the project. The CODEOWNERS file isn't meant to be a strict guideline,
but instead can be used to ease the burden of finding reviewers for a
particular section of the codebase.

It's also possible to enforce that the CODEOWNERS for a particular
file/package sign-off on relevant changes, thereby blocking review
unless they're involved. However, for now we'll simply use it to guide
the review assignment project, leaving creating blocking review
constraints until a later point if deemed useful.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd