Since the slapd data is static and generated using nix, we can simply
move the user list into ops/users, so it's recognized by readTree and we
can use it as ops.users both in ops/nixos/tvl-slapd and web/todolist as
a general purpose user registry for depot.
Update docs/REVIEWS.md as well.
Change-Id: I35caaaab70a5578c47cedc7f33077dd513766290
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2419
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
