Consistent naming: selective replication -> selective sync

doc/administration/geo/replication/configuration.md

@@ -143,7 +143,7 @@ keys must be manually replicated to the secondary node.
    'This is a primary node'.
 1. Optionally, choose which namespaces should be replicated by the
    secondary node. Leave blank to replicate all. Read more in
-   [selective replication](#selective-replication).
+   [selective synchronization](#selective-synchronization).
 1. Click the **Add node** button.
 1. SSH into your GitLab **secondary** server and restart the services:
 

doc/administration/geo/replication/configuration_source.md

@@ -96,7 +96,7 @@ Read [Manually replicate primary SSH host keys][configuration-replicate-ssh]
    'This is a primary node'.
 1. Optionally, choose which namespaces should be replicated by the
    secondary node. Leave blank to replicate all. Read more in
-   [selective replication](#selective-replication).
+   [selective synchronization](#selective-synchronization).
 1. Click the **Add node** button.
 1. SSH into your GitLab **secondary** server and restart the services:
 

doc/administration/geo/replication/index.md

@@ -207,9 +207,10 @@ extra limitations may be in place.
   working on improving this experience, see [gitlab-org/omnibus-gitlab#2978] for details.
 - Real-time updates of issues/merge requests (e.g. via long polling) doesn't work on the secondary
 - Broadcast messages set on the primary won't be seen on the secondary without a cache flush (e.g. gitlab-rake cache:clear)
-- [Selective replication](configuration.md#selective-replication) applies only
-  to files and repositories. Other datasets are replicated to the secondary in
-  full, making it inappropriate for use as an access control mechanism.
+- [Selective synchronization](configuration.md#selective-synchronization)
+  applies only to files and repositories. Other datasets are replicated to the
+  secondary in full, making it inappropriate for use as an access control
+  mechanism.
 
 ### Limitations on replication