pgsql: Add general purpose hasing functions to pgbench.

Add general purpose hasing functions to pgbench.

Hashing function is useful for simulating real-world workload in test like
WEB workload, as an example - YCSB benchmarks.

Author: Ildar Musin with minor editorization by me
Reviewed by: Fabien Coelho, me
Discussion: https://www.postgresql.org/message-id/flat/0e8bd39e-dfcd-2879-f88f-272799ad7ef2@postgrespro.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e51a04840a1c45db101686bef0b7025d5014c74b

Modified Files
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doc/src/sgml/ref/pgbench.sgml                |  59 ++++++++++++++--
src/bin/pgbench/exprparse.y                  |  98 +++++++++++++++++++-------
src/bin/pgbench/pgbench.c                    | 101 +++++++++++++++++++++++++--
src/bin/pgbench/pgbench.h                    |   4 +-
src/bin/pgbench/t/001_pgbench_with_server.pl |  11 +++
5 files changed, 239 insertions(+), 34 deletions(-)