pgsql: Teach pg_dump to dump comments on RLS policy objects.

Teach pg_dump to dump comments on RLS policy objects.

This was unaccountably omitted in the original RLS patch.
The SQL syntax is basically the same as for comments on triggers,
so crib code from dumpTrigger().

Per report from Marc Munro.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/1581889298.18009.15.camel@bloodnok.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6da7d36305a57f6c2fb337898966335fa0f9b0a5

Modified Files
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src/bin/pg_dump/pg_dump.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)