We want to have this in our own monitoring

Disregard ZFS ARC cache when monitoring free RAM

Closes #119

See merge request !331

Monitoring: Add a "Node Exporter Full" dashboard

See merge request !332

, a dashboard that "displays a lot of data about one single host".

This is

One query for hosts with ZFS and one for those without.

Since ZoL frees ARC under memory pressure, let's not
count it as "used" but instead as "free" memory.

Set minimal nixos profile for our grid machines

See merge request !330

First version of borgbackup monitoring dashboard and alerts

See merge request !323

bump nixpkgs version

See merge request !327

Bump megacli version to fix exception handling

See merge request !321

Configure production grid monitoring to also use new 2nd level domain

See merge request !324

refs privatestorageops#416, PrivateStorageio#115

Automatically create production update MRs

See merge request !318

bump nixpkgs version

See merge request !320

Re-add stages

See merge request !317

So expand it ourselves

GitLab docs explicitly say `needs` does not require stages but GitLab actual behavior is:

```
Found errors in your .gitlab-ci.yml:

    update-staging job needs system-tests job, but system-tests is not in any previous stage
    update-staging job needs morph-build-staging job, but morph-build-staging is not in any previous stage

```

Automate updating nixpkgs pin in develop branch once a week

See merge request !305