Improvement: Support Flatbuffers configuration & optimise Config validation

### What

As agreed (Design [PR](https://github.com/eclipse-score/communication/pull/403) is already merged)
+ Config Validation shall be refactored
+ Flatbuffers Configuration shall be supported

### How

Check design for details:
https://github.com/eclipse-score/communication/blob/main/score/mw/com/design/configuration/configuration_refactoring_concept.md

### Estimates for realization

-

### Category

- [ ] Affects Detailed Design

### Requirements / Architecture

- [x] Requirements / Architecture are not affected by this change?

Start with score/mw/com/design/configuration/configuration_refactoring_concept.md and review the merged design PR #403 for the intended configuration changes. Trace the existing Config validation and configuration representation before planning the work. Done means the agreed validation refactoring is implemented and Flatbuffers configuration is supported according to the design.

Written by the indexing model from the issue text.