service/ci: expand on workaround for team#41621

See merge request !50

Normal chunks are okay to backup without any special snapshotting, but
WAL files are written on the fly by Prometheus, and doing a backup
with Bacula will lead to inconsistencies in the storage which can make
recovery more difficult. See also https://github.com/prometheus/prometheus/pull/14317

this should make it easier to jump to the section we want to see.

The anchor has changed, probably because the section was renamed

We seem to be converging over something that covers both flow and
architecture, but even including other mail hosts. It's pretty neat!

See team#41009

Now we have two models: one of email delivery flow, the other of the
redundancy architecture.

Turns out the latter might be clear enough on its own; the main
difference is it omits other mail host snowflakes like lists and the
other mail hosts (gitlab, rt, etc).

See team#41009

This is better, but still hard to read, I'm starting to think I just
need to split this in two diagrams: one to display redundancy and
location, the other for message flow.

This really tells me our naming convention sucks and we should have
picked example0 instead of example-01... But anyway.

This is clunky and overcrowded, but a necessary step to realize we
just can't draw all the lines.

this clarifies the diagram a little bit and starts working on the
clustering design.

This struck me while doing star training with @lelutin: we *do* run
the NRPE checks by hand quite often, and especially
dsa-check-packages. We need to port this to something else eventually.

See: team#40755

This is part of a quote and the square brackets indicate a
reinterpretation of words so it's not meant to be a link to something.

Those are just typos or missing words and shouldn't affect any of the
meaning of the sentences that get changed.