add admin as mongo authsource to properties/connection url

src/main/resources/application.properties

 spring.application.name=todo
 server.port=9876
-spring.data.mongodb.uri=mongodb://${MONGO_USER}:${MONGO_PASSWORD}@${MONGO_HOST}:${MONGO_PORT}/${MONGO_DB}
+spring.data.mongodb.uri=mongodb://${MONGO_USER}:${MONGO_PASSWORD}@${MONGO_HOST}:${MONGO_PORT}/${MONGO_DB}?authSource=admin
 
 #openapi setup
 springdoc.api-docs.path=/v3/api-docs