For fm_well_constraints: retrieve well names from the controls file instead of wells.json

[verveerpj]

Check if fm_well_constraints only uses the well names from wells.json, if so add an option to retrieve those from a json file containing the controls that is stored by Everest.

[verveerpj]

It seems that this forward model needs a field (readydate) in its input wells.json that is not set in the Everest config file. This suggests that this forward model is only used with inputs that are produced by other forward models.

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