DOC: config: fix incorrect section reference about custom log format

DOC: config: fix incorrect section reference about custom log format

Since 2.5 with commit 98b930d043 ("MINOR: ssl: Define a default https
log format"), some log-format sections were shifted a bit without having
been renumberred, causing 8.2.4 to be referenced as the custom log
format while it's in fact 8.2.6. This patch fixes the affected
locations.

In addition two places mentioned 8.2.6 instead of 8.2.5 for the error
log format.

This can be backported to 2.6.