Enhance HTTP resilience by ignoring timeouts for Server-Sent Events

[Hanskrogh]

This pull request enhances the resilience and reliability of HTTP client requests in the AddServiceDefaults extension, especially for Server-Sent Events (SSE). It introduces custom timeout and retry logic for SSE requests, ensuring they are not interrupted by standard timeout or retry policies. Additionally, it includes some minor code cleanups and formatting improvements.

Resilience improvements for HTTP clients:

• Customizes the AddStandardResilienceHandler to detect Server-Sent Event (SSE) requests and disables both attempt and total request timeouts for them, preventing SSE connections from being prematurely closed.
• Prevents retries for SSE requests by customizing the retry policy, ensuring that SSE streams are not retried if they fail.
• Adds a private IsServerSentEventRequest helper method to identify SSE requests by checking for the text/event-stream media type in the Accept header.