Support video views/viewers stats in server

* Add "currentTime" and "event" body params to view endpoint
 * Merge watching and view endpoints
 * Introduce WatchAction AP activity
 * Add tables to store viewer information of local videos
 * Add endpoints to fetch video views/viewers stats of local videos
 * Refactor views/viewers handlers
 * Support "views" and "viewers" counters for both VOD and live videos

shared/models/activitypub/objects/watch-action-object.ts

@@ -0,0 +1,22 @@
+export interface WatchActionObject {
+  id: string
+  type: 'WatchAction'
+
+  startTime: string
+  endTime: string
+
+  location?: {
+    addressCountry: string
+  }
+
+  uuid: string
+  object: string
+  actionStatus: 'CompletedActionStatus'
+
+  duration: string
+
+  watchSections: {
+    startTimestamp: number
+    endTimestamp: number
+  }[]
+}