Use keyword arguments for ApplicationService calls

Not all services are using keywords, which breaks those calls in Ruby 3

app/services/ldap_manager/fetch_avatar.rb

@@ -1,12 +1,11 @@
 module LdapManager
   class FetchAvatar < LdapManagerService
-    def initialize(cn:, ou: nil)
+    def initialize(cn:)
       @cn = cn
-      @ou = ou
     end
 
     def call
-      treebase   = @ou ? "ou=#{@ou},cn=users,#{suffix}" : ldap_config["base"]
+      treebase   = ldap_config["base"]
       attributes = %w{ jpegPhoto }
       filter     = Net::LDAP::Filter.eq("cn", @cn)