Make EQLNUM regions in FlowNet based on region parameter from simulation model

[olelod]

When setting the scheme to regions_from_sim the EQLNUM regions in the input simulation model were used to generate the EQLNUM regions for the FlowNet model. This PR makes this more flexible by allowing any region parameter from the INIT file to be used.

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Contributor checklist

• 🎉 This PR closes #ISSUE_NUMBER.
• 📜 I have broken down my PR into the following tasks:
  • Add region_parameter_from_sim_model to config_parser.py for equil
  • Add checks to config_parser.py
  • Change the generation of EQLNUM regions for FLOWNET to use the region_parameter_from_sim_model instead of the previously hard coded EQLNUM
• 🤖 I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
• 📖 I have considered adding a new entry in CHANGELOG.md.
• 📚 I have considered updating the documentation.