[IMP] base: logging conf & logging of partner merge wizard

* root the base.partner.merge wizard's logger in odoo.addons so the
  "odoo" logger configuration properly applies to it
* update the default logging configuration to set the root logger
  rather than independently set the odoo and werkzeug loggers

closes odoo/odoo#40872

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>