doc(release): prepare release notes for 2021-Q4 release (v1.3)

Signed-off-by: Raphael Defosseux <raphael.defosseux@openairinterface.org>

CHANGELOG.md

 # RELEASE NOTES: #
 
+## v1.3.0 -- January 2022 ##
+
+* Periodic Registration Update
+* Event Exposure Registration
+* Implicit Deregistration Timer
+* Mobile Reachable Timer
+* Validate SMF Info
+* Fix RAN UE NGAP Id
+* Fix SMF Selection SD
+* Fix NSSAI mismatch
+* Fix Service Request
+* Docker optimization
+
 ## v1.2.1 -- October 2021 ##
 
 * Fix build issue