TD-34: Endpoint for getting all players and tests for this endpoint

src/test/java/de/towerdefence/server/IntegrationTest.java

@@ -3,6 +3,7 @@ package de.towerdefence.server;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import de.towerdefence.server.player.Player;
 import de.towerdefence.server.player.PlayerRepository;
+import de.towerdefence.server.player.PlayerService;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.springframework.beans.factory.annotation.Autowired;