Add option to include 'layer' and 'path' attributes in Merge Vector Layers tool (#55397)

[lanckmann]

Description

This pull request addresses Issue #55397 by adding a new option (checkbox) to the Merge Vector Layers processing tool. This option allows users to choose whether to include the layer and path attributes from the individual input vector layers in the resulting merged layer. By default, this option is enabled (true) to maintain backward compatibility.

Changes Made

1. Added a New Boolean Parameter in initAlgorithm()
   • File Modified: qgsalgorithmmergevector.cpp
   • Details: Introduced a new boolean parameter ADD_SOURCE_FIELDS that provides the option to include source layer information (layer and path) in the merged output.

   addParameter(new QgsProcessingParameterBoolean(
       QStringLiteral("ADD_SOURCE_FIELDS"),
       QObject::tr("Add source layer information (layer name and path)"),
       true));
   

[github-actions]

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[qgis-bot]

@lanckmann

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[qgis-bot]

@lanckmann
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

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[qgis-bot]

@lanckmann
A documentation ticket has been opened at qgis/QGIS-Documentation#9455
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
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