Refactor cooperator_website : separate the form controller from the form processor

[robinkeunen]

Is your feature request related to a problem?

• different concerns are mixed together
• testing routes is more complex than testing services

Describe the solution you'd like

• the controller defines the routes and controls data
• the processor handles the business logic based on clean data

Additional context

• using components from oca/connector might be a good idea.

[github-actions]

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