Add option to specify timeout seconds to BackgroundPsql.pm.
Previously, a background psql session uses the default timeout and it
cannot be overridden. This change adds a new option to set the timeout
during start.
There are no users of this new option. It is needed for an upcoming
patch adding tests for XID wraparound.
Reviewed-by: Daniel Gustafsson, Noah Misch
Discussion: https://postgr.es/m/
C9CF2F76-0D81-4C9D-9832-
202BE8517056%40yesql.se