release notes: describe new gRPC based frontend

ReleaseNotes.md

 # v4.NEXT
 
 ## Summary
+
+This release introduced an additional gRPC based frontend for storage backends.
+
 ### Upgrade Instructions
 ### Features
 - cta/CTA#1205 - Fail pipeline if cppcheck detects errors
@@ -10,6 +13,7 @@
 - cta/CTA#1152 - Reduce eos free space query load
 - cta/CTA#1231 - Add --loadtimeout option to cta-tape-label and increase default value
 - cta/CTA#977 - Add --drive option to cta-tape-label
+- cta/CTA#1222 - Add minimal gRPC based forntend for integration with dCache
 
 ### Bug fixes
 - cta/CTA#1120 - Fix negative disk space reservation content