Add sslmode to instructions for replicate-geo-database

Author: Ben Prescott_

doc/settings/database.md

@@ -1197,7 +1197,7 @@ replication user's password.
    command:
 
    ```shell
-   sudo gitlab-ctl replicate-geo-database --slot-name=SECONDARY_SLOT_NAME --host=PRIMARY_HOST_NAME
+   sudo gitlab-ctl replicate-geo-database --slot-name=SECONDARY_SLOT_NAME --host=PRIMARY_HOST_NAME --sslmode=verify-ca
    ```
 
    You will be prompted for the replication user's password of the primary. Replace `SECONDARY_SLOT_NAME` with the slot name retrieved from the first step above.