Add "User-Agent" property to Serilog logging

[marcominerva]

Enhance Serilog logging by including a property named "User-Agent" that contains the User Agent string from the HTTP request, if available. This will improve traceability and diagnostics by identifying the source of requests.

Proposed Solution:

• Update the logging logic to extract the User Agent header from the HTTP request (if it exists).
• Add this value as a property named "User-Agent" in all relevant Serilog log events.

Benefits:

• Easier analysis of traffic patterns and troubleshooting.
• More informative logs for auditing and security review.

Acceptance Criteria:

• The "User-Agent" property is present in log entries when an HTTP request includes a User Agent header.
• If the header is absent, the property should be omitted or set to null/empty.