Move magic symbol into a constant

ee/lib/ee/peek/views/active_record.rb

@@ -11,7 +11,8 @@ module EE
           detail = super
 
           if ::Gitlab::Database::LoadBalancing.enable?
-            role = ::Gitlab::Database::LoadBalancing.db_role_for_connection(data[:connection]) || :unknown
+            role = ::Gitlab::Database::LoadBalancing.db_role_for_connection(data[:connection]) ||
+              ::Gitlab::Database::LoadBalancing::ROLE_UNKNOWN
             detail[:db_role] = role.to_s.capitalize
           end
 

ee/lib/gitlab/database/load_balancing.rb

@@ -143,7 +143,8 @@ module Gitlab
 
       DB_ROLES = [
         ROLE_PRIMARY = :primary,
-        ROLE_REPLICA = :replica
+        ROLE_REPLICA = :replica,
+        ROLE_UNKNOWN = :unknown
       ].freeze
 
       # Returns the role (primary/replica) of the database the connection is