fix: empty string to supported locales to resolve i18n entries within…

[815are]

Issue:

1. create translation entry for "title": "My Itinerary" like -> "title": "{i18n>myItinerary}"
2. update i18n.properties file with new entry

myItinerary=My Itinerary

3. Run preview using cds watch
4. Open preview for travel_processor and navigate to object page;
5. Problem - see myItinerary displayed in preview instead of My Itinerary

Problem is that supportedLocales is defined, but does not contain "" which is used by default when we run preview

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