feat: uninstall empty sections

[williarin]

Fixes #8

This PR introduces a new option for the YAML merger.

Uninstalling YAML recipe

When uninstalling a recipe, the YAML merger will not remove the entire section if it's empty, unless you set the uninstall_empty_sections parameter to true.

files:
    config/routes.yaml:
        type: yaml
        source: |
            other_routes:
                resource: .
                type: other_routes_loader
        uninstall_empty_sections: true

In this example, if the other_routes section is empty, it will be removed when uninstalling the recipe.