Fix a big caching bug. Compatibility with TYPO3 11.4 LTS.

[BUGFIX] Reuse cache entry on related pages (Thanks to Hannes Lau)
[BUGFIX] Fix error in additionalCountries translation handling and simplify code
[TASK] Clear cache after changes in the backend (Thanks to Hannes Lau)
[TASK] Feature flag to disable cache clearing in frontend (Thanks to Hannes Lau)
[TASK] Hint to deactivate EXT:seo hreflang generation (Thanks to Sergio Catalá)
[TASK] Compatibility with TYPO3 11.4LTS