Add Autoconfiguration for OAuth2 + Interface HTTP Clients

It would be nice if Spring Boot added some autoconfiguration for applying Spring Security's OAuth2 Support for Interface HTTP Clients.

The configuration looks like this for RestClient and should be activated with the classpath has RestClient, the OAuth2 client jar, and has an OAuth2AuthorizedClientManager bean.

@Bean
OAuth2RestClientHttpServiceGroupConfigurer securityConfigurer(
		OAuth2AuthorizedClientManager manager) {
	return OAuth2RestClientHttpServiceGroupConfigurer.from(manager);
}

The configuration looks like this for WebClient and should be activated with the classpath has WebClient and OAuth2 client jar, and has an OAuth2AuthorizedClientManager bean.

@Bean
OAuth2RestClientHttpServiceGroupConfigurer securityConfigurer(
		OAuth2AuthorizedClientManager manager) {
	return OAuth2RestClientHttpServiceGroupConfigurer.from(manager);
}

cc @joshlong

Start with the linked Spring Security configuration for RestClient and WebClient, then inspect Spring Boot's existing auto-configuration patterns for conditional classpath and bean checks. Done means the OAuth2 support is activated for the specified client classes and OAuth2AuthorizedClientManager without manual configuration; the issue names no repository files or tests to run.