Clarify log_parameter_max_length docs regarding log_min_duration_statement vs log_duration

Hi,

While reviewing the log_statement_max_length patch [1], I noticed the docs
for log_parameter_max_length say:

This setting only affects log messages printed as a result of
log_statement, log_duration, and related settings.”

However, enabling only log_duration does not log bind parameter values,
so in practice log_parameter_max_length does not seem to affect messages
generated by log_duration. Bind parameters are logged, for example, when
log_min_duration_statement is set.

Given that, referencing log_duration here seems misleading. Would it be
better to mention log_min_duration_statement instead?

I've attached a patch that makes this change.

Regards,

[1] https://postgr.es/m/CA+E0NR4S+NC6+QHyY_vUuQZMzLhKqczMx-jJVqtjAxF6+=JwAA@mail.gmail.com

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Fujii Masao