Subscription types array items should be limited and reference to allowed SubscriptionEventType instead of any string

[dfischer-tech]

Problem description
Subscription types array items should reference to allowed SubscriptionEventType instead of any string link

        types:
          description: |
            Device Quality Indicator event types eligible for delivery by this subscription.
          type: array
          items:
            type: string

Expected behavior

        types:
          description: |
            Camara Event types eligible to be delivered by this subscription for device quality indicators.
            Note: As of now we enforce to have only event type per subscription.
          type: array
          minItems: 1
          maxItems: 1
          items:
            $ref: "#/components/schemas/SubscriptionEventType"

Alternative solution

Additional context