Add search functionality for vocabulary in VocabController and VocabService

- Implemented a new searchVocabs method in VocabService to allow users to search for vocabulary based on learning and mother tongue terms.
- Updated VocabController to include the searchVocabs method wrapped with user authentication.
- Added a new route in vocabRouter for searching vocabulary by language ID.
- Enhanced VocabChapterView and VocabLanguageView components to include a button for opening the search dialog.
- Added translations for search-related terms in both German and English locales, improving user accessibility.

frontend/src/i18n/locales/en/socialnetwork.json

@@ -308,6 +308,16 @@
                 "stats": "Stats",
                 "success": "Success",
                 "fail": "Fail"
+            },
+            "search": {
+                "open": "Search",
+                "title": "Search vocabulary",
+                "motherTongue": "Mother tongue",
+                "learningLanguage": "Learning language",
+                "lesson": "Lesson",
+                "search": "Search",
+                "noResults": "No results.",
+                "error": "Search failed."
             }
         }
     }