Reword docs of feature "Remove temporary files after backend crash"

Hi,

The commit [1] for the feature "Remove temporary files after backend
crash" introduced following in the docs:
+ <para>
+ When set to <literal>on</literal>, which is the default,
+ <productname>PostgreSQL</productname> will automatically remove
+ temporary files after a backend crash. If disabled, the files will be
+ retained and may be used for debugging, for example. Repeated crashes
+ may however result in accumulation of useless files.
+ </para>

The term backend means the user sessions (see from the glossary, at
[2]). It looks like the code introduced by the commit [1] i.e. the
temp table removal gets hit not only after the backend crash, but also
after checkpointer, bg writer, wal writer, auto vac launcher, logical
repl launcher and so on. It is sort of misleading to the normal users.
With the commit [3] clarifying these processes in master branch [4],
do we also need to modify the doc added by commit [1] in PG master at
least?

[1] commit cd91de0d17952b5763466cfa663e98318f26d357
Author: Tomas Vondra <tomas(dot)vondra(at)postgresql(dot)org>
Date: Thu Mar 18 16:05:03 2021 +0100

Remove temporary files after backend crash

[2] PG 14 - https://www.postgresql.org/docs/current/glossary.html#GLOSSARY-BACKEND

[3] commit d3014fff4cd4dcaf4b2764d96ad038f3be7413b0
Author: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Date: Mon Sep 20 12:22:02 2021 -0300

Doc: add glossary term for "auxiliary process"

[4] PG master - https://www.postgresql.org/docs/devel/glossary.html

Regards,
Bharath Rupireddy.