[DOCS] `xpack.ssl.client_authentication` setting does not apply to HTTP (elastic/x-pack-elasticsearch#4113)
Fix the documentation to mention the global setting does not apply to HTTP.
relates elastic/x-pack-elasticsearch#3413
Original commit: elastic/x-pack-elasticsearch@9a19f651688b6a4335cb5ab16941b99d819db29b
@@ -905,7 +905,8 @@ Controls the server's behavior in regard to requesting a certificate
from client connections. Valid values are `required`, `optional`, and `none`.
`required` forces a client to present a certificate, while `optional`
requests a client certificate but the client is not required to present one.
-Defaults to `required`.
+Defaults to `required`. This global setting is not applicable for HTTP, see
+ <<http-tls-ssl-settings>>.
`xpack.ssl.verification_mode`::
Controls the verification of certificates. Valid values are `none`,
