[server] implement dynamic database pooler
Opening too much database connection has a cost at startup and also PostgreSQL
as a maximum number of connection (100 by default).
This get worse when starting multiple wsgi processes, since each process has
its own database pool.
Instead of opening `connections-pool-size` connections to the database at
startup, just open one and open more only when needed.
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