Added Documentation and Unit Tests for HTTP Requests Logging

[mchlkntrv]

This PR adds documentation and unit tests for the last implemented feature of structured HTTP requests logging, along with some other small code fixes.

Documentation updates:

• Added and updated documentation for the new --requests-log-file option, describing its usage and example JSON content.
• Updated the table of contents to include the new HTTP Requests Logging page.

Feature implementation:

• Refactored requests logging configuration and application builder logic to use empty strings instead of nullable types for the requests log file path (to match the existing implementation of log file path resolving ).
• Improved the RequestLogFileEntry model to always provide EndTime and DurationMs as non-null values, since they should never be null.

Testing:

• Added a new test class RequestsLoggingHandlerShould to verify that HTTP requests logging works correctly, including cases for successful requests, failures, missing context, and multiple consecutive requests.

[Burgyn]

Neviem či to takto spájať do jedného testu.
Lebo napríklad by som očakával, že pri testovaní tej exception aj overíme status kód, ...