[server] Make connection pooler configurable and set better default values Drop the configuration connections-pool-size and add new configurations options: * connections-pool-min-size. Set to 0 by default so we open connections only when needed. This avoid opening min-size*processes connections at startup, which is, it think, a good default. * connections-pool-max-size. Set to 0 (unlimited) by default, so we move the bottleneck to postgresql. * connections-idle-timeout. Set to 10 minutes. I don't have arguments about this except that this is the default in pgbouncer.

Tests: unittest
Depends:
 python3-cubicweb, cubicweb-ctl,
 @builddeps@,
 python3-pytest,
 python3-flake8,
 python3-psycopg2, postgresql, postgresql-plpython,
 python3-ldap3, slapd, ldap-utils
Restrictions: allow-stderr, isolation-container

Tests: skeleton-packaging
Depends:
 python3-cubicweb, cubicweb-ctl,
 python3-pyramid, python3-wsgicors,
 devscripts, equivs, lintian, autopkgtest
Restrictions: allow-stderr, needs-root