Add 8.5.5 CHANGELOG items

[ci skip]

CHANGELOG-EE

@@ -9,6 +9,15 @@ v 8.6.0 (unreleased)
   - [Elastic] Use subprocesses for ElasticSearch index jobs
   - [Elastic] More accurate as_indexed_json (More stable database indexer)
 
+v 8.5.5
+  - GitLab Geo: Repository synchronization between primary and secondary nodes
+  - Add documentation for GitLab Pages
+  - Fix importing projects from GitHub Enterprise Edition
+  - Fix syntax error in init file
+  - Only show group member roles if explicitly requested
+  - GitLab Geo: Improve GeoNodes Admin screen
+  - GitLab Geo: Avoid locking yourself out when adding a GeoNode
+
 v 8.5.4
   - [Elastic][Security] Notes exposure