Support TLSv1.3 when running on Java 11

[tvernum]

Java 11 will include support for TLS 1.3.

X-Pack SSL includes specific behaviours around TLS versions including:

• Default values for supported versions XPackSettings.DEFAULT_SUPPORTED_PROTOCOLS
• Configurable version support SSLConfigurationSettings.supportedProtocols
• Mapping those setting strings to TLS algorithm names SSLService.sslContextAlgorithm

Plus we have tests for the above.

Customers who run on Java 11 may wish to enable TLSv1.3, but we

• will reject it as a value in sslContextAlgorithm if it comes before TLSv1.2
• don't test it
• don't document how to enable it

[elasticmachine]

Pinging @elastic/es-security

[Tim-Brooks]

AbstractSimpleSecurityTransportTestCase#testRenegotiation will probably need to be adjusted when we enable TLS 1.3 as I believe that TLS 1.3 does not support renegotiation.