Added post_id filter to activity feed API

fixes https://github.com/TryGhost/Team/issues/2091

- Added new fixtures to make testing easier for the activity feed
- Improved E2E test coverage of activity feed with separate test file
- Added data.post_id filter to enable filtering by events related to a given post

ghost/core/core/server/models/member-click-event.js

@@ -10,7 +10,31 @@ const MemberClickEvent = ghostBookshelf.Model.extend({
 
     member() {
         return this.belongsTo('Member', 'member_id', 'id');
+    },
+
+    filterExpansions: function filterExpansions() {
+        const expansions = [{
+            key: 'post_id',
+            replacement: 'link.post_id'
+        }];
+
+        return expansions;
+    },
+
+    filterRelations() {
+        return {
+            link: {
+                // Mongo-knex doesn't support belongsTo relations
+                tableName: 'redirects',
+                tableNameAs: 'link',
+                type: 'manyToMany',
+                joinTable: 'members_click_events',
+                joinFrom: 'id',
+                joinTo: 'redirect_id'
+            }
+        };
     }
+
 }, {
     async edit() {
         throw new errors.IncorrectUsageError({message: 'Cannot edit MemberClickEvent'});

ghost/core/core/server/models/member-paid-subscription-event.js

@@ -25,6 +25,21 @@ const MemberPaidSubscriptionEvent = ghostBookshelf.Model.extend({
                 .groupByRaw('currency, DATE(created_at)')
                 .orderByRaw('DATE(created_at)');
         }
+    },
+
+    filterRelations() {
+        return {
+            subscriptionCreatedEvent: {
+                // Mongo-knex doesn't support belongsTo relations
+                tableName: 'members_subscription_created_events',
+                tableNameAs: 'subscriptionCreatedEvent',
+                type: 'manyToMany',
+                joinTable: 'members_paid_subscription_events',
+                joinFrom: 'id',
+                joinToForeign: 'subscription_id',
+                joinTo: 'subscription_id'
+            }
+        };
     }
 }, {
     permittedOptions(methodName) {