pgsql: libpq: Align oauth_json_set_error() with other NLS patterns

libpq: Align oauth_json_set_error() with other NLS patterns

Now that the prior commits have fixed missing OAuth translations, pull
the bespoke usage of libpq_gettext() for OAUTHBEARER parsing into
oauth_json_set_error() itself, and make that a gettext trigger as well,
to better match what the other sites are doing. Add an _internal()
variant to handle the existing untranslated case.

Suggested-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/0EEBCAA8-A5AC-4E3B-BABA-0BA7A08C361B%40yesql.se
Backpatch-through: 18

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f7fbd02d32c46ee1cada6c3faf94414657b7a19a

Modified Files
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src/interfaces/libpq/fe-auth-oauth.c | 31 +++++++++++++++++++------------
src/interfaces/libpq/nls.mk          |  2 ++
2 files changed, 21 insertions(+), 12 deletions(-)