Since b9cfbcafdf, the lack of hexdump in
the closure lead to the generation of empty cookie files. This empty
cookie file is making pleroma to crash at startup now we correctly
read it.
We introduce a migration forcing these empty cookies to be
re-generated to something not empty.
We inject the release cookie path to the pleroma derivation in order
to wrap pleroma_ctl with it. Doing this allows us to remove the
systemd-injected RELEASE_COOKIE path, which was sadly
buggy (RELEASE_COOKIE should point to the *content* of the cookie, not
the file containing it).
We take advantage of this to factor out the cookie path.
As the only consequence of isSystemUser is that if the uid is null then
it's allocated below 500, if a user has uid = something below 500 then
we don't require isSystemUser to be set.
Motivation: https://github.com/NixOS/nixpkgs/issues/112647
