[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.
3.28
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Changes
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- the class cubicweb.view.EntityAdapter was moved to cubicweb.entity.EntityAdapter
a deprecation warning is in place, but please update your source code accordingly.
- The database pooler is now dynamic. New connections are opened when needed and closed after a configurable period of time. This can be configured through `connections-pooler-max-size` (default 0, unlimited), `connections-pooler-min-size` (default 0), and `connections-pooler-idle-timeout` (default 600 seconds). The old configuration `connections-pooler-size` has been dropped.