Exposed parameter backuptype from aiven's api (#1111)

Author: shivamp296

specification/resources/databases/models/backup.yml

@@ -12,6 +12,11 @@ properties:
     type: number
     example: 0.03364864
     description: The size of the database backup in GBs.
+  incremental:
+    type: boolean
+    example: false
+    description: >-
+      Indicates if this backup is a full or an incremental one (available only for MySQL).
 
 required:
   - created_at

specification/resources/databases/responses/database_backups.yml

@@ -45,8 +45,10 @@ content:
       backups:
       - created_at: '2019-01-11T18:42:27Z'
         size_gigabytes: 0.03357696
+        incremental: false
       - created_at: '2019-01-12T18:42:29Z'
         size_gigabytes: 0.03364864
+        incremental: true
       scheduled_backup_time:
         backup_hour: 20
         backup_minute: 40