Consume clang-format config file from central repository

### What

https://github.com/eclipse-score/inc_diagnostics/pull/19 introduced a clang-format config file based on what `score-baselibs` defined. Since source code formatting shall not deviate between the various score repositories, it should instead get consumed from a central other repo (e.g. `score-cpp-policies`)

### Acceptance Criteria (DoD)

- clang-format config file gets referenced from a central repo (i.e. `score-cpp-policies`)
- the local clang-tidy file introduced in https://github.com/eclipse-score/inc_diagnostics/pull/18 got removed again from the `inc_diagnostics` repository

### How

_No response_

Start by reviewing pull requests #19 and #18 to identify the local clang-format and clang-tidy files and how they are referenced in inc_diagnostics. Check the corresponding integration or configuration in score-cpp-policies. Done when formatting uses the central repository and the local clang-tidy file is removed.

Written by the indexing model from the issue text.