You can use iCloud Photos. However, iCloud Photos is a syncing system as explained in this article:
Set up and use iCloud Photos - Apple Support
But be aware that iCloud Photos is not offline storage. Photos and videos that you delete on your iPad will also be deleted everywhere that you use iCloud Photos (including iCloud). To save space on your iPad, see the "Save space on your device" section in the above article.
If you really want offline storage you will need a third party solution such as google drive. Or you can transfer them to a computer:
Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support