[scripts][databases_provider] Add parameter to specify configuration section to load

With the current implementation, the configuration of the
execution process may contain two entries:
1) Main algorithm
2) Loop algorithm

The way the databases provider works will only load the main
entry which means that it will use the wrong configuration
for the loop algorithm. This new parameter allows to set
which entry should be used to configure the database. The
default is None so the default behaviour doesn't change.
2 jobs for improve_database_executor in 4 minutes and 33 seconds (queued for 4 seconds)