MINIFICPP-2594 Add XMLReader controller service

[lordgamez]

• Upgrade pugixml library to v1.15

https://issues.apache.org/jira/browse/MINIFICPP-2594

Depends on #1999

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[Copilot]

Pull Request Overview

This PR adds XMLReader controller service functionality to Apache NiFi MiNiFi C++ and upgrades the pugixml library from v1.9 to v1.15.

• Implements a new XMLReader controller service for parsing XML content into Record objects
• Upgrades pugixml library to v1.15 and modernizes the build system to use FetchContent instead of ExternalProject
• Updates build configurations to use the new pugixml library target

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
extensions/standard-processors/controllers/XMLReader.h	Defines XMLReader controller service class with properties for XML parsing configuration
extensions/standard-processors/controllers/XMLReader.cpp	Implements XML parsing logic and record creation functionality
extensions/standard-processors/tests/unit/XMLReaderTests.cpp	Comprehensive test suite covering various XML parsing scenarios
cmake/PugiXml.cmake	New CMake module for fetching pugixml v1.15 using FetchContent
cmake/BundledPugiXml.cmake	Removes old ExternalProject-based pugixml build configuration
extensions/standard-processors/CMakeLists.txt	Updates to link against new pugixml target
extensions/windows-event-log/CMakeLists.txt	Updates WEL extension to use new pugixml target
CMakeLists.txt	Includes new PugiXml module for standard processors and WEL extension
CONTROLLERS.md	Documents the new XMLReader controller service properties

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[fgerlits]

I think we need to add pugixml to the NOTICE file, as well.

Also, TinyXml2 is listed in both the LICENCE and NOTICE files, but we don't use it (any more?) -- it can be removed.