fix(s3): document options for adjusting multipartcopy behavior

Added in nextcloud/server#41914

Signed-off-by: Josh <josh.t.richards@gmail.com>

admin_manual/configuration_files/primary_storage.rst

@@ -195,6 +195,8 @@ Optional parameters less commonly needing adjustment:
 * :code:`timeout` defaults to :code:`15`
 * :code:`uploadPartSize` defaults to :code:`524288000`
 * :code:`putSizeLimit` defaults to :code:`104857600`
+* :code:`useMultipartCopy` defaults to :code:`true`
+* :code:`copySizeLimit` defaults to :code:`5242880000`
 * :code:`legacy_auth` has no default
 * :code:`version` defaults to :code:`latest`
 * :code:`verify_bucket_exists` defaults to :code:`true` [Note: Setting this to :code:`false` *after* confirming the bucket has been created may provide a performance benefit, but may not be possible in multibucket scenarios.]