[2810] Allow private config to override output directories and filename

[evenmn]

Description

Adds optional private_config overrides for model, log, and results directories, plus the output filename. Explicit directories are used directly, without appending the run ID. Existing defaults remain when overrides are omitted.

path_shared_working_dir: /work/weathergen

path_model: /models/deployed
path_logs: /var/log/weathergen
path_results: /forecasts
output_name: forecast.zip

Checkpoint loading and logging use the selected private configuration.

Issue Number

Closes #2810

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Checklist before asking for review

• I have performed a self-review of my code
• My changes comply with basic sanity checks:
  • I have fixed formatting issues with ./scripts/actions.sh lint
  • I have run unit tests with ./scripts/actions.sh unit-test
  • I have documented my code and I have updated the docstrings.
  • I have added unit tests, if relevant
• I have tried my changes with data and code:
  • I have run the integration tests with ./scripts/actions.sh integration-test
  • (bigger changes) I have run a full training and I have written in the comment the run_id(s): launch-slurm.py --time 60
  • (bigger changes and experiments) I have shared a hegdedoc in the github issue with all the configurations and runs for this experiments
• I have informed and aligned with people impacted by my change:
  • for config changes: the MatterMost channels and/or a design doc
  • for changes of dependencies: the MatterMost software development channel

FastEvaluation

• I have updated the public documentation if necessary

[clessig]

@grassesi : could you also have a look?

[clessig]

@evenmn : could you lint please :)

[clessig]

Thanks, this is a useful feature. Some minor comments. We also should merge this into the preops branch.

[evenmn]

@clessig Thank you for the comments. Please have a look at my answers and latest commits