Update the CODEOWNERS file with some people who joined different parts
of the project, and one person that left.
Note that despite is name, CODEOWNERS does not list "ownership" in any
strict sense of the word - it is more about who is willing and/or
knowledgeable enough to participate in reviewing changes to particular
files or directories. Github uses this file to automatically suggest
who should review a pull request.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#12216
f275bfd57b