Introduce ClientHttpConnectorBuilder support

Add a new `ClientHttpConnectorBuilder` interface to support the
creation of `ClientHttpConnector` instances. The new code is similar
to the `ClientHttpRequestFactoryBuilder` interface that was added to
Spring Boot 3.4.

The `ClientHttpConnectorBuilder` is a functional interface with
additional static factory methods for the various supported
`ClientHttpConnector` types. Each type has it's own builder
which to support client specific customization.

The previous auto-configuration has been relocated to the
`org.springframework.boot.autoconfigure.http.client.reactive`
package and updated to make use of the builder.

Closes gh-43079

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/io/rest-client.adoc

@@ -52,6 +52,45 @@ You can learn more about the {url-spring-framework-docs}/web/webflux-webclient/c
 
 
 
+[[io.rest-client.webclient.configuration]]
+=== Global HTTP Connector Configuration
+
+If the auto-detected javadoc:org.springframework.http.client.reactive.ClientHttpConnector[] does not meet your needs, you can use the configprop:spring.http.reactiveclient.settings.connector[] property to pick a specific connector.
+For example, if you have Reactor Netty on your classpath, but you prefer Jetty's javadoc:org.eclipse.jetty.client.HttpClient[] you can add the following:
+
+[configprops,yaml]
+----
+spring:
+  http:
+    reactiveclient:
+      settings:
+        connector: jetty
+----
+
+You can also set properties to change defaults that will be applied to all reactive connectors.
+For example, you may want to change timeouts and if redirects are followed:
+
+[configprops,yaml]
+----
+spring:
+  http:
+    reactiveclient:
+      settings:
+        connect-timeout: 2s
+        read-timeout: 1s
+        redirects: dont-follow
+----
+
+For more complex customizations, you can use javadoc:org.springframework.boot.autoconfigure.http.client.reactive.ClientHttpConnectorBuilderCustomizer[] or declare your own javadoc:org.springframework.boot.http.client.reactive.ClientHttpConnectorBuilder[] bean which will cause auto-configuration to back off.
+This can be useful when you need to customize some of the internals of the underlying HTTP library.
+
+For example, the following will use a JDK client configured with a specific javadoc:java.net.ProxySelector[]:
+
+include-code::MyConnectorHttpConfiguration[]
+
+
+
+
 [[io.rest-client.webclient.customization]]
 === WebClient Customization