[BUG - Dev] Scenario Users not being added correctly

[louispt1]

Bug Description

Adding ScenarioUsers in MyETM does not link the users correctly to their engine scenarios, despite myetm reflecting the scenario users as collaborators/viewers/owners.

The bug comes from users' emails and ids not being linked in the created ScenarioUser objects.

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Where is it happening

Engine Pro. You can see in the inspect controller that scenario users are not added to the scenarios, and via the api.

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Type of Issue

What type of dev issue is this?
Select all that apply:

• User Experience
• Unintuitive design
• Calculation
• API
• Tests
• Other

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Expected Behaviour

ScenarioUsers should be linked with all available information (id & email or the max subset).

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Current Behaviour

Currently the ScenarioUser model couples users by their id, even though the params from myetm actually pass the user email

def couple_existing_user
    return unless user_email.present? && user_id.blank?
    couple_to(User.find_by(id: user_id))  # Looks up by user_id 
  end

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Steps to Reproduce

Modify the steps to fit your case

1. Add any user as a viewer,collaborator or owner in myetm on a saved scenario
2. Go to the saved scenario - you will see the user has appeared in myetm.
3. Go to the scenario in the engine, look at the scenario users - nothing will have changed
4. Check the engine db - a user is created with no id, but an email address (the pending user case)