Upgrade to NixOS 22.11

Closes #126 and #141

See merge request !387

It passes us more arguments and it requires us to give each test definition a name.

error: anonymous function at PrivateStorageio/nixos/tests/private-storage.nix:1:1 called with unexpected argument 'system'

Fix Textcollector alert message typo

See merge request !391

Docs: Add monitoring and alerting infrastructure diagram

See merge request !390

Add Zulip alerting

Closes privatestorageops#455

See merge request !389

Thanks @bendon!

.. that I forgot earlier.

Switch to new zkapauthorizer that works with NixOS 22.11.
Since we're not a flake yet we have to add a few work-arounds
as well.

Increase load15 alert to only fire if it's over 1 for 2 hours or more

See merge request !388

Recently this alarm fired a couple of times when the backup self-
check ran.

Set it to alert only when load is over 1 for longer than 2 hours.

Crank up borgbackup log level to INFO (from default WARN)

Closes #136

See merge request !385

Rotate my SSH key for the testing grid

See merge request !386