Update nixpkgs.

See merge request !193

Protocol sequence diagrams for ZKAPs

See merge request !190

now that default.nix is actually somewhat useful

`cp --recursive ...` is required for permission issues
`... --out-link result-docs` is required for path collision issues
the rest is at my discretion

Monitoring dashboards: Rethink scales

Closes privatestorageops#24

See merge request !189

Add a nixos module for the ZKAP Spending Service

See merge request !172

Simplify local grid hardware

See merge request !182

This changes the Throughput graph to be relative, changes its unit
to Bit/s, and fixes the labels of the Network pkt/s graph.

Fixes privatestorageops#24.

Metric names: It's vouchers (plural)

See merge request !187

Make payment server answer with a 404 by default

See merge request !186

[Copy pasta](https://whetstone.privatestorage.io/privatestorage/PrivateStorageio/-/blob/ca44204076983ce02fd3e0dacd940514e0821e23/nixos/modules/spending.nix#L130) - Thanks @tomprince!

Enable alerting

Closes privatestorageops#392

See merge request !185

Epiphany: Systemd reads more than a single environment file. This
lets me improve the file naming much.

Unfortunately still prints a bold warning on deployment.

This will store the supposedly secret URL in the Nix Store and
print a honking big warning about it.

Use `networking.fqdn` to define `targetHost`, rather than constructing it ourselves.

See merge request !183

Update nixpkgs.

See merge request !181

Set nixpkgs explicitly in morph.

Closes #85

See merge request !174

Only dashboards in this dir