fix: Override merging behaviour

[warcooft]

Description
This PR improves how configuration values are merged during registrar discovery. Previously, nested configuration arrays (e.g., globals['before']) were being overwritten because the merging process used array_merge(), which only works at the top level. As a result, any registrar attempting to append or modify nested config values would unintentionally replace the entire subtree.

This ensures that nested configuration arrays are merged correctly without overwriting existing keys, providing more predictable and safer behavior for external packages and modules that rely on registrars.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[neznaika0]

See #9231 and #9445

[neznaika0]

We didn't make the right decision. And this is BC, in 4.7 with the update of the docs and tests.
I think we should just discuss it in the existing issue.

[warcooft]

See #9231 and #9445

We didn't make the right decision. And this is BC, in 4.7 with the update of the docs and tests. I think we should just discuss it in the existing issue.

Understandable, thankyou!