feat: deep merge imports to combine local and catalog configs

[JordanGoasdoue]

What issue type does this pull request address?

/kind feature

What does this pull request do? Which issues does it resolve?

Implements recursive deep merge for config imports to allow projects to inherit shared catalog configs while only overriding specific values.

Problem:
When importing a config (e.g., from a git catalog), the current implementation only does a shallow merge at the first level. If both the imported config and the local config define the same section (like dev.api), nested maps are completely replaced instead of being merged.

Example:

# Catalog
dev:
  api:
    labelSelector:
      app: catalog-app
      version: v1
    command: ["/bin/bash"]

# Local config
dev:
  api:
    labelSelector:
      app: my-app

Before: Local labelSelector replaces catalog entirely → loses version: v1
After: Maps are deep merged → keeps both app: my-app and version: v1

Solution:

• Maps: deep merged recursively (local overrides on conflict)
• Arrays: local replaces catalog entirely
• Scalars: local overrides catalog

This enables the common use case where organizations maintain a shared catalog in git, and projects only need to override specific values (like app name) while inheriting everything else (ports, sync config, commands, etc.).

Please provide a short message that should be published in the DevSpace release notes

Imports now use deep merge for map fields, allowing projects to inherit shared catalog configs while only overriding specific nested values. Arrays and scalars continue to be replaced entirely by local config.

What else do we need to know?

• Added comprehensive test coverage with 5 test cases covering real-world scenarios
• Backward compatible: existing configs will continue to work as before
• All existing tests pass

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