Update TestRestTemplate's default cookie handling to match RestTemplate's

[apoorvdarshan]

Summary

• TestRestTemplate previously disabled cookies by default (StandardCookieSpec.IGNORE), differing from RestTemplate which uses the HTTP client library's default
• Aligns the defaults so TestRestTemplate no longer explicitly ignores cookies
• Adds withCookies(HttpCookies) method for explicit cookie control, following the same pattern as withRedirects(HttpRedirects) from Align TestRestTemplate default redirect settings to be the same as RestTemplate #43431
• Introduces HttpCookies enum, HttpComponentsCookieSpec adapter, and cookies() on RestTemplateBuilder
• Deprecates HttpClientOption.ENABLE_COOKIES

Fixes gh-48607

Test plan

• TestRestTemplateTests — verifies default cookie spec is now null (library default), withCookies(ENABLE) returns "strict", withCookies(DISABLE) returns "ignoreCookies"
• HttpClientSettingsTests — verifies withCookies() and updated orElse() with cookies field
• HttpClientAutoConfigurationTests — verifies settings construction with new record shape
• Existing redirect tests remain green

[wilkinsona]

Thanks for the PR, @apoorvdarshan. In addition to the two comments I've made, I think some changes to the various other …HttpClientBuilder classes are missing. The required changes will be similar to the changes that you've made for HttpComponentsHttpClientBuilder to honour the cookies configuration.

[apoorvdarshan]

Thanks for the review feedback @wilkinsona! Both items addressed:

1. Updated the ENABLE_COOKIES deprecation to "for removal in 4.3.0"
2. Added an explicit deprecated four-argument HttpClientSettings constructor that delegates to the new five-argument canonical constructor to preserve backward compatibility

[wilkinsona]

Thanks. Did you see this additional comment?

I think some changes to the various other …HttpClientBuilder classes are missing. The required changes will be similar to the changes that you've made for HttpComponentsHttpClientBuilder to honour the cookies configuration.

[apoorvdarshan]

Thanks for pointing that out! I've added cookie handling to the other builders:

• JdkHttpClientBuilder: Maps HttpCookies to a CookieHandler — ENABLE/ENABLE_WHEN_POSSIBLE sets a CookieManager, DISABLE leaves the default (no cookie handler)
• JettyHttpClientBuilder: Maps HttpCookies to a HttpCookieStore — DISABLE sets HttpCookieStore.Empty, ENABLE/ENABLE_WHEN_POSSIBLE keeps the library default (cookies enabled)

Reactor Netty's HttpClient doesn't have automatic cookie management at the transport level, so no changes were made there.