Add integration test for elasticsearch

[arnosthavelka]

• https://github.com/spring-projects/spring-data-elasticsearch/blob/main/src/test/java/org/springframework/data/elasticsearch/junit/jupiter/SpringIntegrationTest.java
• https://www.testcontainers.org/modules/elasticsearch/ (referenced by https://stackoverflow.com/questions/67801883/how-to-do-spring-data-elastic-search-integration-tests)
• https://github.com/spring-projects/spring-data-elasticsearch/blob/main/src/test/java/org/springframework/data/elasticsearch/core/LogEntityTests.java

[arnosthavelka]

CityIntegrationTest with testcontainers is added , but not finished.

[arnosthavelka]

there's a new @DataElasticsearchTest annotation -> see https://docs.spring.io/spring-boot/docs/current/reference/html/features.html#features.testing.spring-boot-applications.autoconfigured-spring-data-elasticsearch