Add proposition mixin to AEP Web SDK ExperienceEvent mixin

[Aaronius]

We need to add the Proposition Interaction mixin, which was provided in https://github.com/adobe/xdm/pull/1139, to the AEP Web SDK ExperienceEvent mixin. Adobe Experience Platform Web SDK will use these fields to notify when personalized content has been rendered or interacted with.

What are the schemas that are affected by the issue

https://ns.adobe.com/experience/aep-web-sdk-experienceevent Github URL: https://github.com/adobe/xdm/blob/master/extensions/adobe/experience/aep-web-sdk-experienceevent.schema.json

What are examples of products that are impacted by the issue

Adobe Experience Platform Web SDK will be populating these fields, which will affect Target and Offer Decisioning.