pgsql: gss: add missing references to hostgssenc and hostnogssenc

gss: add missing references to hostgssenc and hostnogssenc

These were missed when these were added to pg_hba.conf in PG 12;
updates docs and pg_hba.conf.sample.

Reported-by: Arthur Nascimento

Bug: 16380

Discussion: /messages/by-id/20200421182736.GG19613@momjian.us

Backpatch-through: 12

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ac5852fb3042a4562e8a8bab26aaa00fa8183068

Modified Files
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doc/src/sgml/client-auth.sgml | 28 ++++++++++++++--------------
src/backend/libpq/pg_hba.conf.sample | 14 +++++++++-----
2 files changed, 23 insertions(+), 19 deletions(-)