Update nixpkgs.

See merge request !207

Update zkapauthorize to use mach-nix and nixos-21.05.

See merge request !166

Weekly nixpkgs updateUpdate nixpkgs.

See merge request !205

Weekly nixpkgs update.

See merge request !204

Fix dev docs for repo update script

See merge request !203

Thanks @jcalderone for pointing me to it

Alerting: Only alert when an exporter is not scrapable for 5 mins or longer

See merge request !200

This change reflects my intention of having an alert fire when a node
is not scrapable for five minutes or longer.  I hadn't understood the
default avg() function well enough before, yielding an alert that would
fire too soon (i.e. any time a node was down, even only one minute for a
reboot).

Use `$__file{}` for grafana's slack URL secret.

See merge request !191

Weekly nixpkgs update.

See merge request !199

Monitoring: Add dashboard and alerting for used swap

Closes privatestorageops#358

See merge request !198

Alerting: Don't when no scraping error ever happened.

See merge request !197

Use a version of vulnix that doesn't collapse derivations with different sets of patches.

See merge request !196

Update PaymentServer.

See merge request !195

Expose zkap-spending-service metrics.

See merge request !184

Fixes privatestorageops#358.

Monitoring: Add dash for scraping failures + alert

Closes privatestorageops#355

See merge request !188

- The serivice can be reached by other machines.
- The metrics cannot be reached by other machines.

Don't use our nixpkgs fork for LeaseReport.

Closes privatestorageops#373

See merge request !192

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