[App Configuration] - Head request support

[linglingye001]

Added new public methods to ConfigurationClient

• public virtual AsyncPageable<ConfigurationSetting> CheckConfigurationSettingsAsync(SettingSelector, CancellationToken)
• public virtual Pageable<ConfigurationSetting> CheckConfigurationSettings(SettingSelector, CancellationToken)

that send HTTP HEAD requests to check for configuration setting changes without retrieving the full response body. This feature enables efficient watching scenarios by reducing bandwidth usage while still allowing clients to detect changes via response headers.

[Copilot]

Pull request overview

This PR adds HEAD request support to the Azure App Configuration client, enabling efficient change detection for configuration settings without retrieving full response bodies. The new methods CheckConfigurationSettingsAsync and CheckConfigurationSettings use HTTP HEAD requests to check if settings have changed by examining response status codes and headers (like ETags) while minimizing bandwidth usage.

Key Changes:

• Added CheckConfigurationSettingsAsync and CheckConfigurationSettings public methods that return pageable collections with empty Values but populated response headers
• Implemented ParseCheckConfigurationSettingsResponse to extract pagination tokens from Link headers without parsing response bodies
• Added comprehensive test coverage for both modified and unmodified scenarios, including validation that 304 responses don't trigger warnings

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
sdk/appconfiguration/Azure.Data.AppConfiguration/src/ConfigurationClient.cs	Adds new public Check methods and supporting infrastructure including CheckConfigurationSettingsPageableImplementation helper and ParseCheckConfigurationSettingsResponse parser
sdk/appconfiguration/Azure.Data.AppConfiguration/tests/ConfigurationLiveTests.cs	Adds 6 test methods covering async/sync variants for unmodified pages, modified pages, and warning log validation scenarios
sdk/appconfiguration/Azure.Data.AppConfiguration/assets.json	Updates test assets tag to reflect new test recordings

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Azure.Data.AppConfiguration