dialvia: do not send default GO HTTP client User-Agent

[Choraden]

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[what-the-diff]

PR Summary

• Inclusion of Empty Header Field to the req Object
  The update introduces an empty 'Header' field to the 'req' object. This is earmarked for future uses and ensures additional data can be manipulated or included as necessary.

• Addition of User-Agent Header to the req Object
  The pull request adds a 'User-Agent' to the 'req' object. This identifier will inform the server about the technology (web browser, mobile browser, applications, etc.) that initiates the request, assisting in the delivery of an optimized user experience contextually.

• Direct Addition of Proxy-Authorization Header to the req Object
  Instead of building a new 'http.Header' object, we now directly add the 'Proxy-Authorization' header to the 'req' object. It's an efficient technique that reduces unnecessary creation of objects and optimizes resource usage.

• Conditional Inclusion of ConnectRequestModifier to req Object
  Revised code now only adds 'ConnectRequestModifier' to the 'req' object if it's not null. This prevents unnecessary operations on an absent entity, enhancing the code's efficiency and overall performance.