Command pg_dump not found

This always happens due to Odoo can't find where are postgresql_client installed(if it's True that is installed, perhaps you have no instalation of this packages or Odoo have no user rights to access it).

You could config the exact location of your pg_path where the postgresql_client tools are located. This could be done in your config file used to launch Odoo adding

pg_path = /path/to/postgresql/bin