Add array_merge_if helper function for conditional array merging

[altas-innova-tech]

This PR adds a new array_merge_if helper function that conditionally merges arrays based on a boolean condition.

Motivation

Currently, conditional array merging requires verbose if-else blocks or ternary operators, making code less readable:

// Current approach
$config = $isProduction 
    ? array_merge($baseConfig, $prodConfig) 
    : $baseConfig;

// With array_merge_if
$config = array_merge_if($isProduction, $baseConfig, $prodConfig);