EnableHttp2PublicAPI

[xinlian12]

Changes

Added public API to enable http2 in beta version.

• Added new class Http2ConnectionConfig, where customer can config maxConnectionPoolSize, minConnectionPoolSize, isEnabled, and maxConcurrentStreams

Http2ConnectionConfig http2ConnectionConfig = new Http2ConnectionConfig()
                .setEnabled(true)
                .setMaxConnectionPoolSize(10)
                .setMinConnectionPoolSize(1)
                .setMaxConcurrentStreams(30);
            gatewayConnectionConfig.setHttp2ConnectionConfig(http2ConnectionConfig);

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

com.azure:azure-cosmos

[FabianMeiswinkel]

LGTM except for few comments