pgsql: Improve user control over truncation of logged bind-parameter va

Improve user control over truncation of logged bind-parameter values.

This patch replaces the boolean GUC log_parameters_on_error introduced
by commit ba79cb5dc with an integer log_parameter_max_length_on_error,
adding the ability to specify how many bytes to trim each logged
parameter value to.  (The previous coding hard-wired that choice at
64 bytes.)

In addition, add a new parameter log_parameter_max_length that provides
similar control over truncation of query parameters that are logged in
response to statement-logging options, as opposed to errors.  Previous
releases always logged such parameters in full, possibly causing log
bloat.

For backwards compatibility with prior releases,
log_parameter_max_length defaults to -1 (log in full), while
log_parameter_max_length_on_error defaults to 0 (no logging).

Per discussion, log_parameter_max_length is SUSET since the DBA should
control routine logging behavior, but log_parameter_max_length_on_error
is USERSET because it also affects errcontext data sent back to the
client.

Alexey Bashtanov, editorialized a little by me

Discussion: https://postgr.es/m/b10493cc-a399-a03a-67c7-068f2791ee50@imap.cc

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0b34e7d307e6a142ee94800e6d5f3e73449eeffd

Modified Files
--------------
doc/src/sgml/config.sgml                      | 62 +++++++++++++-----
src/backend/nodes/params.c                    |  2 +-
src/backend/tcop/postgres.c                   | 57 ++++++++++------
src/backend/utils/mb/stringinfo_mb.c          |  6 +-
src/backend/utils/misc/guc.c                  | 34 +++++++---
src/backend/utils/misc/postgresql.conf.sample |  7 +-
src/bin/pgbench/t/001_pgbench_with_server.pl  | 93 ++++++++++++++++++++++++---
src/include/utils/guc.h                       |  5 +-
src/pl/plpgsql/src/pl_exec.c                  |  4 +-
9 files changed, 207 insertions(+), 63 deletions(-)