Add @type or @context (or both) properties to Mercure data when object is deleted

**Description**
Currently, the data of the Mercure update contains only the IRI of the removed object inside the `@id` property. This is enough for cases where topics are created for specific collections or items. More generic topics containing updates for several collections force the subscriber to parse the IRI to identify the affected collection. Unfortunately, for some collections, this requires writing a code which is difficult to maintain. An example of such an issue would be a collection of `Person` entities. The prefix for such entities is `/people/`. Adding the `@type` in the case of update/create events would make it easier for the subscriber to identify the affected collection.

**Example**
The `data` of the event would change from:
```
{"@id":"\/people\/1ed69b32-4697-68fc-9f20-e17dcbef2976"}
```
to:
```
{"@type":"Person", "@id":"\/people\/1ed69b32-4697-68fc-9f20-e17dcbef2976"}
```

I can create a PR if this is accepted.