Minor config fixes

[valentin-krasontovitsch]

Issue
Related generally to #3740, and more specifically to #2567.

Approach
In these two commits we

• set two default values in the python path for model config
• include the number of realizations parameter in the dict setup for config testing

Pre review checklist

• Added appropriate release note label
• PR title captures the intent of the changes, and is fitting for release notes.
• Commit history is consistent and clean, in line with the contribution guidelines.

Adding labels helps the maintainers when writing release notes. This is the list of release note labels.

[valentin-krasontovitsch]

btw: default values are taken from fmu-docs, list of all keywords

[eivindjahren]

🚀

[valentin-krasontovitsch]

github action running the ert tests keeps failing with different stuff - first it was a flaky / randomy test (#3870), then it was a timeout, the tests took longer than 30 minutes to run and got cancelled... restarted now.