Training examples initialization script (rebased onto dev_5_0)



This is the same as gh-2561 but rebased onto dev_5_0.

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As part of the ongoin effort to unify/run the trainings examples, this PR adds a first version of a CLI script which populates a server with a training user/group and some example data. 
Together with this PR, the merge-integration job will be rewritten to:
- run the population script against the integration server to create data
- generate a `training_ice.config` file populated with the credentials/object ids

Then the training job should:
- consume the config file created by the integration job
- run the various example scripts using this configuration file

/cc @jburel

                    
Fair enough. I hardcoded it to let it pass but there is no reason not to configure it. Arguably, we could also set it up in the job to include the job number e.g. `training_user_298`.