pgsql: psql: Add more information about service name

psql: Add more information about service name

This commit adds support for the following items in psql, able to show a
service name, when available:
- Variable SERVICE.
- Substitution %s in PROMPT{1,2,3}.

This relies on 4b99fed7541e, that has made the service name available in
PGconn for libpq.

Author: Michael Banck
Reviewed-by: Greg Sabino Mullane
Discussion: /messages/by-id/6723c612.050a0220.1567f4.b94a@mx.google.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/477728b5d6fa16461b81cd22b0568fec1eab97ac

Modified Files
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doc/src/sgml/ref/psql-ref.sgml | 14 ++++++++++++++
src/bin/psql/command.c | 2 ++
src/bin/psql/prompt.c | 6 ++++++
3 files changed, 22 insertions(+)