net/http: add debug logging for HTTP/1 client transport

[yorukot]

This change introduces a set of debug logging features for HTTP/1 client
Transport, similar to those already present for HTTP/2. It includes
environment variable initialization for logging levels and functions
to log requests, responses, and connection events.

The change improves observability and helps diagnose issues in HTTP/1
connections by enabling optional, verbose logging.

Updates #18733

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