Fix RestClient to use defaultRequest on RestClient.Builder

[injae-kim]

Closes gh-32028

Motivation

• On DefaultRestClientBuilder.defaultRequest(...) doesn't do anything #32028 , we found that DefaultRestClientBuilder.defaultRequest(...) doesn't do anything
  • Cause RestClientBuilder.build() doesn't pass defaultRequest to RestClient

Modification

• Fix RestClient to use defaultRequest on RestClient.Builder

Result

• Now RestClient uses defaultRequest that passed from RestClientBuilder.build() well

[injae-kim]

spring-framework/spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClient.java

Lines 481 to 484 in faba044

	private ClientRequest.Builder initRequestBuilder() {
	if (defaultRequest != null) {
	defaultRequest.accept(this);
	}

FYI) almost same usage of defaultRequest on WebClient~!

[poutsma]

Superseded by 0ada78a.