Add root config file support for analysis tuning and improve SoMEF failure handling

[vuillaut]

This PR addresses fixes #85 by allowing users to configure RsMetaCheck similarly to linters, via a repository-level config file.

It also improves the SoMEF failure experience by stopping early when no outputs are produced, instead of continuing into a misleading empty analysis.

What changed

1. Added repository-level analysis configuration support.
2. Added config-driven controls for:
   • ignored pitfalls/warnings
   • per-check parameters
   • excluded metadata source files
3. Added profile support (for example unstable/dev vs prerelease) to enable different strictness levels by context.
4. Wired config through CLI and analysis execution so detector behavior is actually parameterized.
   Improved failure behavior:
   • if SoMEF produces no JSON outputs, analysis is aborted with an actionable error
   • clearer message for invalid/insufficient GitHub token scope issues
5. Updated documentation with usage examples.
6. Added tests covering config path/profile forwarding, behavior changes from config, and SoMEF-empty-run abort logic.

Validation

• Targeted pytest suites passed for CLI/config/e2e and relevant detector tests.

Impact

• Backward compatible for users without config files.
• Enables CI workflows to use stricter prerelease profiles and more tolerant unstable/dev profiles without code changes.

[vuillaut]

Note: we can discuss if we want to have configurable thresholds or not. We could also be opinionated on this.