Add JettyClientHttpConnector that accepts a HttpClient instance and a JettyResourceFactory

[philwebb]

See spring-projects/spring-boot#16810 for background.

Currently JettyClientHttpConnector has the following constructor:

public JettyClientHttpConnector(
		JettyResourceFactory resourceFactory, @Nullable Consumer<HttpClient> customizer) {
	HttpClient httpClient = new HttpClient();
	httpClient.setExecutor(resourceFactory.getExecutor());
	httpClient.setByteBufferPool(resourceFactory.getByteBufferPool());
	httpClient.setScheduler(resourceFactory.getScheduler());
	if (customizer != null) {
		customizer.accept(httpClient);
	}
	this.httpClient = httpClient;
}

This allows us to apply settings to the HttpClient from the resourceFactory and apply additional customization. Unfortunately, the only way we can change the sslContextFactory is when constructing the HttpClient (we can't use the customizer). This means we're forced to copy/paste the code that applies theresourceFactory items.

Could we please have an additional constructor that takes a HttpClient instance and still applies the JettyResourceFactory settings.