Borgbackup:  Accept unknown hosts

Closes #118

See merge request !302

Simplify Grafana used memory query

See merge request !304

June 13 2022 nixpkgs bump

See merge request !303

node_memory_MemAvailable_bytes is a better estimator than the sum I used before
says some Prometheus documentation.  It is also almost the same, but reads nicer.

Fixes #118

nixpkgs update 2022-05-23

See merge request !301

Borgbackup

Closes privatestorageops#314

See merge request !297

Reword SSH private key for CD docs

See merge request !296

Grafana Resources Dashboard: Add user cipher text panel

See merge request !295

Avoid an nginx timeout on the redemption endpoint

See merge request !299

This reverts commit c8a13555.

Sadly, Borg says this is not a good idea: https://borgbackup.readthedocs.io/en/stable/faq.html#can-i-backup-from-multiple-servers-into-a-single-repository

Spoiler:  This won't work, Borg does not guarantee consistency with
parallel writers to the same repo as I now found out.