MDL-49399 task: Add admin log viewer

AMOS BEGIN
 CPY [eventstarttime,core_calendar],[task_starttime,core_admin]
 CPY [eventduration,core_calendar],[task_duration,core_admin]
 CPY [result,core_cache],[task_result,core_admin]
 CPY [database,install],[task_dbstats,core_admin]
 CPY [fail,install],[task_result:failed,core_admin]
AMOS END

lib/classes/task/database_logger.php

@@ -84,6 +84,29 @@ class database_logger implements task_logger {
         $logdata->id = $DB->insert_record('task_log', $logdata);
     }
 
+    /**
+     * Whether this task logger has a report available.
+     *
+     * @return  bool
+     */
+    public static function has_log_report() : bool {
+        return true;
+    }
+
+    /**
+     * Get any URL available for viewing relevant task log reports.
+     *
+     * @param   string      $classname The task class to fetch for
+     * @return  \moodle_url
+     */
+    public static function get_url_for_task_class(string $classname) : \moodle_url {
+        global $CFG;
+
+        return new \moodle_url("/{$CFG->admin}/tasklogs.php", [
+                'filter' => $classname,
+            ]);
+    }
+
     /**
      * Cleanup old task logs.
      */