Add upgrade guide for 8.2 to 8.3
Making sure we don't forget mentioning the need to upgrade Redis from !1888 (merged). Added this in preparation for 8.3.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Making sure we don't forget mentioning the need to upgrade Redis from !1888 (merged). Added this in preparation for 8.3.