Added CollectionPost events

refs https://github.com/TryGhost/Arch/issues/95

These events can be used to know when an automatic collections posts have been
updated, as well as by the repository to optimise the storage of
CollectionPosts

ghost/collections/src/events/CollectionPostAdded.ts

@@ -0,0 +1,19 @@
+type CollectionPostAddedData = {
+    collection_id: string;
+    post_id: string;
+};
+
+export class CollectionPostAdded {
+    data: CollectionPostAddedData;
+    timestamp: Date;
+    type = 'CollectionPostAdded' as const;
+
+    constructor(data: CollectionPostAddedData, timestamp: Date) {
+        this.data = data;
+        this.timestamp = timestamp;
+    }
+
+    static create(data: CollectionPostAddedData, timestamp = new Date()) {
+        return new CollectionPostAdded(data, timestamp);
+    }
+}

ghost/collections/src/events/CollectionPostRemoved.ts

@@ -0,0 +1,19 @@
+type CollectionPostRemovedData = {
+    collection_id: string;
+    post_id: string;
+};
+
+export class CollectionPostRemoved {
+    data: CollectionPostRemovedData;
+    timestamp: Date;
+    type = 'CollectionPostRemoved' as const;
+
+    constructor(data: CollectionPostRemovedData, timestamp: Date) {
+        this.data = data;
+        this.timestamp = timestamp;
+    }
+
+    static create(data: CollectionPostRemovedData, timestamp = new Date()) {
+        return new CollectionPostRemoved(data, timestamp);
+    }
+}

ghost/collections/src/index.ts

@@ -4,3 +4,5 @@ export * from './Collection';
 export * from './events/PostAddedEvent';
 export * from './events/PostEditedEvent';
 export * from './events/TagDeletedEvent';
+export * from './events/CollectionPostAdded';
+export * from './events/CollectionPostRemoved';