pgsql: Add a check_hook for output_plugin_libraries

Add a check_hook for output_plugin_libraries

I omitted explicit syntax validation of output_plugin_libraries in
226e49cbed. [ALTER SYSTEM] SET does this implicitly due to the parser
grammar, but a DBA could still accidentally put a bad value into
postgresql.conf, and a superuser could do the same with connection
options or set_config(). Logical replication would then fail later on.

This is an annoying papercut for a security option to have, so reject
these cases immediately in a check_hook.

Tests by Hayato Kuroda.

Co-authored-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Reported-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Discussion: https://postgr.es/m/CAOYmi%2BkBsG5rNRb1j2VjgTKg8HY90e7vSvZPLeouiAc6nXP9XA%40mail.gmail.com
Backpatch-through: 14

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/161d5ffcc5c2f446df528bd273de822b86965d92

Modified Files
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src/backend/replication/logical/logical.c | 46 ++++++++++++++++++++++++-------
src/backend/utils/misc/guc_parameters.dat | 1 +
src/include/utils/guc_hooks.h | 2 ++
src/test/regress/expected/guc.out | 4 +++
src/test/regress/sql/guc.sql | 3 ++
5 files changed, 46 insertions(+), 10 deletions(-)