🐛 Fixed email analytics crashing when processing unsubscribe/complaint events (#14883)

refs https://github.com/TryGhost/Team/issues/1649

The event handlers for `unsubscribed`/`complained` events originating from Mailgun were still using the now-deleted `member.subscribed` field resulting in errors and aborted attempts at processing the Mailgun event log.

- `member.subscribed` no longer exists, replaced that part of the query with a delete of member<->newsletter association rows from the `members_newsletters` pivot table
- kept the member `updated_at` bump so we have some timestamp record of an update
- added creation of `member_subscribe_event` records for the newsletter unsubscribes to keep stats and history in check
  - the unsubscribed/complained events do or at least should originate from a member action so "member" is more appropriate than "system" even though the event is being handled by an internal system

core/server/services/email-analytics/lib/event-processor.js

@@ -1,4 +1,5 @@
 const {EventProcessor} = require('@tryghost/email-analytics-service');
+const {default: ObjectID} = require('bson-objectid');
 const moment = require('moment-timezone');
 
 class GhostEventProcessor extends EventProcessor {
@@ -130,33 +131,43 @@ class GhostEventProcessor extends EventProcessor {
     }
 
     async handleUnsubscribed(event) {
-        const memberId = await this.getMemberId(event);
-
-        if (!memberId) {
-            return false;
-        }
-
-        const updateResult = await this.db.knex('members')
-            .where('id', '=', memberId)
-            .update({
-                subscribed: false,
-                updated_at: moment.utc().toDate()
-            });
-
-        return updateResult > 0;
+        return this._unsubscribeFromNewsletters(event);
     }
 
     async handleComplained(event) {
+        return this._unsubscribeFromNewsletters(event);
+    }
+
+    async _unsubscribeFromNewsletters(event) {
         const memberId = await this.getMemberId(event);
 
         if (!memberId) {
             return false;
         }
 
+        const subscribedNewsletterIds = await this.db.knex('members_newsletters')
+            .where('member_id', '=', memberId)
+            .pluck('newsletter_id');
+
+        await this.db.knex('members_newsletters')
+            .where('member_id', '=', memberId)
+            .del();
+
+        const nowUTC = moment.utc().toDate();
+        for (const newsletterId of subscribedNewsletterIds) {
+            await this.db.knex('members_subscribe_events').insert({
+                id: ObjectID().toHexString(),
+                member_id: memberId,
+                newsletter_id: newsletterId,
+                subscribed: false,
+                created_at: nowUTC,
+                source: 'member'
+            });
+        }
+
         const updateResult = await this.db.knex('members')
             .where('id', '=', memberId)
             .update({
-                subscribed: false,
                 updated_at: moment.utc().toDate()
             });