feat: Allow DNS zones with trailing dot

[fsandel]

Description

The problem was the STACKIT DNS API strips the trailing dot of the DNS name of the zone.
Fixed this problem by trimming the trailing dot on the request to the API, but keeping it in the terraform state to stay in sync with the config.

relates to #1083

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Acceptance tests got implemented or updated (see e.g. here)
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)