pgsql: Improve version reporting in pgbench.

Improve version reporting in pgbench.

Commit 547f04e73 caused pgbench to start printing its version number,
which seems like a fine idea, but it needs a bit more work:
* Print the server version number too, when different.
* Print the PG_VERSION string, not some reconstructed approximation.

This patch copies psql's well-tested code for the same purpose.

Discussion: https://postgr.es/m/1226654.1624036821@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/84bee9610965331d5110971d8de390a5bbe2effc

Modified Files
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src/bin/pgbench/pgbench.c                    | 36 +++++++++++++++++++++++++++-
src/bin/pgbench/t/001_pgbench_with_server.pl |  2 +-
2 files changed, 36 insertions(+), 2 deletions(-)