[confmap] - new feature flag for append merging strategy

[VihasMakwana]

Koanf's default merging strategy currently overrides static values such as slices, numbers, and strings. However, lists of components should be treated as a special case. This pull request introduces a new feature gate to allow for merging lists instead of discarding the existing ones.

With this new merging strategy:

• Lists under the service configuration are merged rather than replaced.
• The merging logic is name-aware, meaning that if components with the same name appear in both lists, they will only appear once in the final merged list.
• This strategy only affects configurations under service::*.

Link to tracking issue

Related issues:

• Append components flag #8754
• Allow instantiating extensions in separate configs #8394
• [ConfMap] - Providing custom merge method for koanf's Map.Merge #10370

Testing

• Added

Documentation

• To be added

Note: I’d appreciate your feedback on this 🙏